Have been doing this for a year or so on some mini-gigs myself (sax'n'trax), and agree with you on most of the wish list, especially RESTS, my main handicap in putting intros/ending together.

I found it helpful to put a volume pedal between the device and the amp for a little bit of dynamic control, it helps. I also back off the piano and drums some in relation to the bass, I find it's a little easier on the ears long-term.

It is truly an amazing piece of software, definitely not complaining either!