Great series, Dave. The crops are fine, as far as I'm concerned. I think some of your problem with contrast and "pop" is light: it's very flat light, diffused from (I take it) overhead, which of course tends to flatten things. Not much you can do about that, unless you want to go strobist on us. D5000 will remotely trigger a Speedlight, right? Put one on a stand.
The compositions are pretty good, I think, except that the drummer appears to have that "I can't move my head" style. Some drummers are apparently taught, or decide themselves, that they should keep their bodies and heads still while their hands move. I'm a drummer, but I have no idea why some people do this. This guy appears especially stiff, but if you say he's a fill-in, maybe he's just trying to concentrate.
I love 3 & 4. The guitar player in 1 is great: I might crop out the drummer. 5 doesn't work for me, I think because it's ambiguous whether he's looking at the neck or off into the distance: I don't know where he's looking, so what's the shot about? 6, 7, 11, and everything with the drummer look as if no one's having fun: 11 almost looks pensive, but doesn't quite make it. 8 is a nice shot, but not much to grab attention, to be honest. The reflections are too muted, and the action on the guitar isn't anything special: better at a slower shutter speed, maybe, to show some blur? 10 is a nice treatment, but not a good pose, looking down.
I like the two you added as happier - much more energy there. And I love the B&W: it looks like something from the 1948 Nashville Gazette, if there is such a thing.
Cheers,
Rick