If we go to the bottom of it, no one needs anything. Personally there are character features (in their progression) and/or certain spells that I would find pleasing to roleplay with or use. The answer to "What is unlocked after 14 that makes a character more unique and more satisfying to roleplay? Especially for a character who isn't a combatant." would be very similar to "What is unlocked after level 4, for a non-combatant?". Or any arbitrary level you decide on, when going at it.
Character progression to me, as a thing on it's own, feels rewarding. I like and enjoy that feeling of achievement when you progress towards a new level or you manage to achieve it, and you in turn unlock new features regarding to your character class. And RP XP, feels like an appropiate way to reward spending a great deal of time roleplaying instead of grinding or killing monsters for XP. It ties both together.
I don't choose that level arbitrarily. Capping the server at 4 or 10 would lock us out of a lot of fun flavour feats only found here, not to mention prestige classes. Also, in my post, I outlined how most of the endgame content is still doable, save for maybe one very specific dungeon, but it can still be done in a way that the server considers traditional: ninjalooting. And the ninjalooter can have a party come with him. The dungeon could be rebalanced later if it's a severe loss, but none of the dungeons found in Sithicus are particularly long.
At level 14 you can be a 7/7 fighter/weaponmaster, a 5/9 Bard/RDD, all sorts of stuff. At the same time, while you can have all this flavour, while you're
capable of completing all of the content on the server (effectively making 15+ nothing more than victory lap levels or post-enchanting levels), you don't become invincible, or even really strong enough to be disruptive. AMPCs start out one level below you, but will level up over time to close that gap.
They could also potentially be allowed to keep going past the normal character cap, so, if you want to take them on alone, you'll have to do it through roleplay or bring a huge group of people to even contend against them, and that will lead to casualties as a level 16 MPC is usually more than a match for a level 16 PC, even with enchanted gear. Depending on monster type, class, and build, of course. This would drastically reduce consequence-free ganking them into irrelevance, which may not be a huge problem, but it potentially could be. At any moment, high level players could feel spited, and they could go and gank those MPCs, who generally walk a tightrope from the day they are made, to the day they are finished. Some MPCs survive only because of the mercy of their opposition, too, and almost all of them must find ways to avoid, stall, or prolong conflict so that the story can go on for the many. This would be easier if they weren't outleveled by a good number of players that could change their mind about leaving them alive at any time.
I totally agree that it's fun to adventure with others, it's a great way to unwind and just kill some time on the server rather than playing another unrelated game. But there is progression even if you are not leveling up past 14. You're gaining money and you're spending time with your mates, learning synergy with them. You're getting used to using your spells and abilities, learning to position better, and so on. It also reduces the likelihood of huge level disparity in a party that leads to what are essentially carries, rather than a character being a guide to a dangerous area.
(edit: fixed this missing section) I think RP XP is great, I just don't see why someone has to progress to near-epic levels of power at all. And if they are going to, I think it's great that they'd like to do it over months and months of roleplay XP, as I've said before, there's really no problem with that. But there's also no clear indicator as to why they need those levels. That's the crux of my point, it's that mainly that no one really has to be above level 14, not even to be a capable, accomplished adventurer in the scope of the server, and certainly not any kind of noncombatant.
This is a difficult situation, it's why we talk about it so much, but I want to highlight the impossibility of what essentially boils down to, "high level characters remove tension/ruin roleplay/trample MPCs/make low levels feel useless, so let more high levels be made through RP XP." The unfairness of a high level ganking an MPC does not suddenly change just because there's more high levels around, in fact there's no evidence it won't get worse if the MPCs can't even really threaten anyone except the players who have their characters submit despite being high enough level to fight back with good odds of victory.
To add to the above post on the topic of what levels add... I am probably not the only one who feels this way:
For those of us who are more hardcore roleplayers, who aren't chasing levels for pure power or combat fun, builds and a lack of levels can nevertheless affect our roleplay. Consider for example the healer who spends all his time roleplaying being a healer, who focuses on nothing else, who doesn't run off to dungeon in the mists all the time, and who is capped at level 14. Level 19 Mist Camp dungeoner comes in, throws down a heal roll or a heal spell, and continues on their day.
Theoretically the RP XP exists for people like the healer, whose roleplay should over time lead them to be a better healer.
Can you spot the problem?
It's happened to me, and I've seen it happen to others (for all sorts of skills or situations). It was a frequent point of sadness for me on my Morninglordian who regularly tended the temples and engaged in learning how to heal and practicing healing, only for people with the benefit of dungeons and extended RP XP to come in and be so much better.
A level 14 character can obtain a heal skill of 17, 3 more from the skill focus, not counting their wisdom modifier or any items they have.
A level 14 character can also cast Heal. More than once, at that. Mass Heal, even, if they're using the Salvation domain. They can cast Regenerate and grow back a limb on a whim, or use Resurrection to return an impaired corpse to life.
So, no, I don't really see the problem. In fact, on my high level cleric, who asks about a person's health status before making a move to heal them, I've seen lower level characters walk up and throw a heal roll or spell at them, before the person being asked even responds to me.
I don't think that's a problem, or that it's not what a hardcore roleplayer would do. People will do as they do, and we don't have to be the first or the best to be valid. Your character's level didn't lead to you being sidelined in those situations, and neither did my character's level have anything to do with my situation; sometimes other people are doing the same thing you want to do. Having peers is okay, it does not diminish what you're doing at all.
The point of some of the content in my previous post was to point out that a higher level can mentor that lower level. It's entirely unnecessary to ruin someone else's fun, yet sometimes, whatever level we are, we do exactly the thing someone else was hoping we didn't. Accepting that our characters will meet others on their journey who will become their peers, betters, subordinates, pupils, and so on, is how factions and other groups can coexist at all, especially factions which are destined to pull in a lot of characters whose function is the same, like the Children of the Morninglord, who are healers and defenders of sacred places. If there are 3 Clerics in the faction, the highest level one is not the only one who matters, and may not even be the one most suited to being a healer, and that's totally okay. Mentorship is how a lot of people get into the groove of a prestige class too, and all the same, the student of the mentor is not invalid during the period in which they are learning from the mentor.
Because for all this, my healer has done surgery on people, at the pew closest to the door in the outskirts temple on packed days, even inviting help from other characters, who did not walk up with their Heal potions or start spamming spells and rolls to take over. If someone walks up and asks you, "Doc, what's taking so long?" you can remind them entirely IC that rushing a procedure is a bad idea, not unlike the way a doctor would respond in real life. I've had great experiences being a low level learning from higher levels, and I've also opened up my high level characters to learning from lower levels. So I do not personally identify this as a recurring enough problem to factor into my suggestion to lower the cap, or my observation that almost nobody who is a noncombatant actually needs to be able to obtain a level in which they are so far above any fresh AMPC they are basically no longer threatened.
I use the level 14 as a goalpost because of other reasons mentioned earlier in this post, and earlier posts, e.g. dungeon completion, challenge of encounters found on the road, and spell availability/metamagic balance. So while it may seem off topic, it has everything to do with the RP XP level cap, which I've never once expressed agreement with, but at the same time, it reminds me that level 15 and up don't really seem to add much.