Instead of always syncing down they could sync the dungeon and lower level players to the higher level of that content. And the lower level players could get temporary access to the higher lv skill/spells! Like anything 16-49 would be Lv50 like anything 51-59 would be Lv60 and 61-69 would be Lv70 and there could be a setting for this like there is for the undersized party and stuff!