Keep the XP system in place where you get less xp for higher levels hanging around. This is that stops them from just carrying lower leveled PC's everywhere, unless it's for raw information, which is okay.
Just to make sure you understand how things now work: lower levels get less XP when monsters are killed near high levels. The RP system works differently, and it is the high levels who suffer.
Used to, the average level in an area was calculated, and high levels received less RP XP if the average was too low. The Devs kept insisting this was working as it intended, to rebut the substantial majority of players who, when given a chance, expressed they wanted it removed.
Despite saying it was working as they intended and their data showed that, the Devs responded by no longer tying it to average character level but to geographical area. So who you are RPing with no longer affects the XP earned.
I'm not going to repeat all my arguments about why this was a dreadful change--probably the worst change I've seen implemented here--but I do have a new one: this change makes it harder to draw crowds for strictly RP events that are unlikely to involve any Challenge Rating at all.
If an event like the Cornell lectures is held in an "RP rich" zone, then low levels have difficulty attending. They must travel through dangerous areas and away from their natural base. Afterward, they have to return.
If such an event is held in an "RP poor" zone, then the high levels have less incentive to attend it, and if they do, they're going against the segregation being OOCly enforced upon us.
Trying to revitalize, for example, the Broken Bell is going to be hard if high levels (who tend to be the most dedicated players on the server and the kind who would devote consistent time to something like rehearsing and performing) know they won't get any XP for their devotion to the project.
Meistersinger was three hours of high-quality RP that any high levels in attendance had to do purely out of altruistic dedication.