A certain amount of high levels will always congregate in the outskirts simply because it allows you to be tougher than most people around you. This is a thing in every game I've ever played. In shooters, people make new "smurf" accounts once they're experienced at the game to go back and bash on new players still learning so they can look like pros. On Ark and Rust, some fully kitted people don't use their gear and levels to explore the high-yield resource areas, they go to the starter areas and walk around shooting people, expending much more in resources than they actually gain from looting the dead. In Elite: Dangerous and other MMOs there's always the guys in the end-game ship or gear cruising around the starter areas to hear the "oohs" and "ahhs" of weaker players who haven't done the 1000 hour grind yet. Some people just like being a big fish in a small pond. Even if you literally gave them real life money to go elsewhere, they probably wouldn't, because then they don't get to be "super cool level 20 guy" and they have to instead go hang out somewhere that level 9 spells don't impress people. Or somewhere that they can't just KD spam anyone who calls them a doo doo head.
To me, it's a problem more specific to the players involved, not the "risk vs reward" or whatever else you want to throw out there. This is 100% a mindset issue with some players just wanting to be "Pope Cool Guy MD, attorney at law" 24/7 and they can't do that as easily when surrounded by people of similar level because they lack the tact/creativity/skill to actually stand out in an even playing field. These players aren't ever going to change because they do an amazing job of thinking they're not part of "that" group of players. They're probably reading this post right now going "yeah i hate those guys." Could be worth taking a good look at yourself and why you're in an area, and if you're high level, asking "Can I move this elsewhere, and would it add to the experience/atmosphere for lower level people who can't yet venture elsewhere safely?"
To the RP XP reduction, I never really felt like it majorly affected things one way or another. I also never based where I choose to RP on whether or not I get XP from it. I RP for the reward of the RP itself, I do dungeons when I want to get xp. As I stated before, I also don't think it affects the Dr Cool Guy crowd either because they'd probably be willing to LOSE xp just to be a high level in a low level area. In my opinion, the people it does affect is the "optimal" crowd. The people who play this game like it's a race to get to level 20 and base their decisions mostly around how they can get more xp, gold, and gear. For what it's worth, if the XP reduction really does only keep these guys away from the outskirts and new players, I'd probably be fine with that and call it "working as intended"
As for those suggestions, Port doesn't make sense for every character, which is why some people just don't go there. But there are plenty of "inclusive events" going on. As a matter of fact, there's an entire civil war happening and it's very easy to get involved. I walked there on a character I haven't played in like a year last week and already got involved in 2 separate events because I talked to people, offered services ICly, and didn't stand off to the side silently being a big [crosses arms]. I always see a lot of people complaining about not being able to get into stuff, but I also see a lot of PCs who never speak to anyone outside their very small circle of friends. I'm not a diviner, but I'd say those two things might be related. Also if you want to join the theatre or try to work at a cafe or something, you could always.... try to do that? People have done it in the past, it's entirely possible. I'm sure Arawn or one of the other DMs who are active in port would be glad to help you bring more RP to the area, but the thing is, you need to bring more to the table than "I want to hand drinks to people in the X inn." Make it an RP thing, have goals, make it "fun" for a DM to want to endorse and dedicate some time or effort to. The Miner's Merriment crew area a sterling example of how to turn a very simple concept into a living, breathing area that people WANT to go hang out at. Maybe get in touch with those guys for ooc pointers.
There is nothing stopping anyone from going out to higher level areas and doing things. People just don't want to put in the leg work. Starting things up is rough, it'll be slow at first. It takes driven and dedicated people to really make endure long enough to gather a regular following. Gavril Valentin stood at the "Plum" Bridge between Ionelus and Wachter territory for like 3 or 4 months doing checks, searches, and RP every day before the faction really started booming and he got company out there.
The point I'm trying to make here is that in my own opinion, I think it really has nothing to do with "not enough incentive" or "reduced XP" or whatever else was mentioned here. Some players just like being around weaker characters and lower level monsters. A lot of people don't want to put the effort into building something new, and there's a lot more "RP Infrastructure" in the lower level areas with more factions, merchants, and PCs congregating. I doubt adding the RP XP reduction really made that big of an impact outside of forcing a very select group elsewhere, but I also think that if it was removed, we'd see even more high levels directly in the outskirts since they don't have to go to the Wayfarer lodge or other high-average-level zones to get RP XP. That's the real issue here, is that it applies by area instead of larger zones. You can just go inside a building and the average level there is now much higher since all the new PCs running around didn't go in there.
Edit - Also, since it keeps coming up for some reason, Harbinger was level 13, only making 14 from RP XP JUST before he died, and had no enchanted items at all. Last time Soren posted the stats, the average level for the outskirts was 12. And most of the people I ended up fighting were usually higher level than I was, in a group of 10 or so people, and would use the ML temple as a safe haven, escape, or rest/rebuff mid fight zone. Also the WFK base was less than 30 seconds away so those guys showed up basically every time within the first minute or two of a scene. I wouldn't really say I had a huge advantage or was "quite a few levels above the cutoff." And definitely not when compared to most of the people I had to deal with when I went to that area.