I can only speak for myself of course, but I use RealTracks for the final production.
I used to produce and mix local bands, and compared to their almost unsalvageable trainwrecks of recordings , RealTracks are REALLY good.
Good as in "professional musicians recorded by a professional sound engineer".
Some of them need a little love to shine, but in general they are very usable.
And if I can't find anything suitable for the song at hand, I can still record my own stuff.
By giving them a little love, I am assuming that you mean adding EQ, saturation, delay, etc. As you say, nothing is stopping one from recording their own tracks. And that seems to be the nice thing about BiaB, you don't have to take every track.