I don't pay much attention to the quest level, just enjoy the show. But I have all 8 classes and do every quest I can find as well as getting the zone discovered reward.
As for repeating the same quests on different classes, cool with me, as each character plays and responds differently.
I also played wow from vanilla with multiple characters, but the difference was once you cleared the starting zones it was all pretty much the same.
Lastly, regarding being over-powered due to grey quest issues, I just accept that it's my destiny to be awesome, and I don't like being killed *lol*
But I can understand the OP and others concerns, but this is a new mmo and ignoring the 'but wow did it this way & its 2011/2012", I believe BW will improve the game / fix issues - and some will like the change and others will hate it.