The thing is, most of this discussion focuses on the guild xp nerf for questing. How much guild experience does running a heroic with 4+ guildies get you? I don't know, but it's probably more than 30 mins of max lvl quests, which, since they give no experience to you, you get none for the guild. (At least I think this is the case.) If most of your members are done leveling, then run some dungeons together, do things as a guild!
I'm assuming a few runs of heroics or raids a day will easily get you the cap on guild exp, but if they don't: ignore this post.
Edit: Hell, the guild exp from leveling exp was probably just put in in order to keep guilds moving along at the start of cata. It'd feel really wierd to have five quested 85s and still be guild lvl 1.