Ninja looting isn't actually a problem, I don't think. The treasure respawns extremely quickly compared to creature spawns, and the quality of the treasure doesn't deteriorate as long as the creature spawn is left alone. The point I was making with the loot tables is that the loot is a lot better in the new player areas than in the higher level areas, and a successive distribution would be beneficial for exploration.
If you are an "adventurer who has escaped the life of a commoner", then likely your "goals and dreams" are to get rich so that you may one day retire. Either that, or you're a thrill seeker. What I would deem a suitable adventure for a party in the 9-12 range has much much worse loot than an adventure for a party in the 5 - 8 range, and only slightly worse loot for than an adventure for a party in the 1- 4 range. For extremely risky encounters suitable for a party of level 13's to 16's, you can expect your reward to be vases worth 10 gold, Warrior's Sashes, Scrolls of less than 3rd level, and stacks of gold under 100 coin. As far as loot is concerned currently, your ultimate adventure ends at Mount Baratak, and you have very little reason to go anywhere else unless you're just grinding experience points.
The Dev team seems to be working on this, as I've noticed there's a lot less treasure in the Werewolf caves than there used to be, meaning that the design is for higher level encounters to be worth more from a GP standpoint, and they are slowly balancing out areas aimed at lower levels to be worth less from a GP standpoint, as it should be. I think when the quality of treasure and craftable resources increases in gradual increments as you move away from Vallaki, we will start seeing more people migrate towards the Mist Camp, and RP like PC Merchants and new Faction Bases will develop naturally out of a player population being present.
Overall, it's not the worst thing in the world for higher level PC's to return to Vallaki, since canonically it is a major trade city right in the middle of the Old Svalich Road. Heretic's point of high levels hanging out in the Outskirts brooding, and disrupting plots aimed at low levels is a very valid one though, and higher level PC's should realize that everyone needs to have a good time, and some adventures are tailored for certain levels, even non-DM run ones. Again, I'd like to compliment Mordsch and single him out for being awesome about avoiding lowbie events and areas for any reason other than Roleplay.
P.S. The Sullen Woods loot spawns need to go the way of the Fisher.