It is a change of pace, which even if it were 10% of the pace of questing, would be decent.
It's a game, so we play for having fun. If BG's are fun, that's good enough for me.

I like that you can skip some quests, move on to the next area.
And still be at (or about) where you would have been, if you had done everything.
BG's and instances give that to us.