Rather than a level cap which turns away anyone outside the specific parameters of that area, I'd prefer they just scale down the level of the higher level characters to match the intended level of the behest. Characters under such a level cap restriction would keep all of their skills, but their stats would be scaled down to match the intended level of the behest. Naturally, completion of the behest or leaving the zone the behest is in will cause the level cap restriction to be removed.
Additionally, some kind of NPC Pearl telling you when a behest was going on and in what area so people could more easily participate in them and didn't feel as though they have to camp one specific region because they might miss out on the behest if they left.
I prefer a scaling down effect to a straight restriction because I like my behests to be populated with plenty of people so that it feels more like a war, and less like a skirmish. That, and not being able to play = not much fun.
Edited, Jan 25th 2011 12:06am by WarkupoZ
I for one would appreciate the idea of rank scaling, since that would actually increase the difficulty of the Behest and reduce the feeling of zerg-fest :-) Even so, there's still the odd person or two - the one who's in the Behest but isn't in the main party (an oversight, easily done,) who then engages the mobs (and getting excellent SP) which are not engaged to our party while going in /say "(Party) (Please invite me.)" 'sigh'
With the Behests, a Warden will appear every hour at every Aetheryte Camp/Gate that offers leves, and an automated message that repeats every minute will appear in local if you're around the camp area. Most people will know this already, and newer players will learn it very soon :p