In my opinion, audio over A2DP can either sound OK or crappy... never great.
That's my experience. I mostly use it to listen to podcasts, and for that it's obviously far more than adequate (podcasts are so compressed already). But when I play music it sounds fine to me.
I would be interested to learn what devices actually support AVRCP v1.4 right now.
There's never been a whole lot of interest/support in this area in general. I think the best any car company, for example, has done would be Ford and Microsoft's Sync, which I believe will look at your collection somehow. I'm not sure what it's using for that, though.
I'm still waiting for someone to make a decent simple remote for bluetooth devices (for play/pause, FF, REW, etc).