This one is always hard, because the most enticing reward would be stat based buffs, but then that would kill new players coming into a server. I think in one similiar post, i put together a couple of kdeas, the main to would balance the OP stats of server settlers by allowing to transfer a level 60 directly over to a new one.
IE when you remove bracelet, you get 15 extra att points (not a huge advantage 405 v 390), x number of extra feat points (and lets you buy 5 levels ahead of time), or you can transfer a level 60 to the same type of server ( ex PvP to PVP only). The feat and att points would be given at beginnig, essentially starting you with 1 perk or recipe.
You would have an icon (hopefully not causing lag ) by your id. letting people know you have completed the game on the server.
After completeing the game three times on one server, you could have bonus feats and atts, and then jump servers (losing the bonus feats and stats, those are server based only)
And for aesthetics, you get a special cosmetic looking armor ( armor stats on par with highest in the same category, light, med, heavy) that you can make 1 time on each restart (when you hit level 60), and give it a + 9 on stat of your choice, along with temp setting of you choice, + heat, + cold, or none. This armor can be looted as well on servers that allow looting.