Are these the portraits you were talking about Dave? I got the (probably mistaken) impression you were doing something more formal...
Aanyway The images here (and through on Flickr) all give the impression you're "part of the audience". The worst culprit for me is the side-on capture. Compare them to "Pretty Lady" and "The Drummer" on your Flickr which have much more engagement. Your last shot of Sam Brown is also pretty good. Can you get in front, or closer? There's not much going on below the elbow. Next time - how about trying landscape and getting in a bit closer, leaving some room for them to sing into? Just an idea.. Also - try and grab moments. End of the song usually gets a smile when people clap. Watch out for emotion in the music. Grab the facial expressions then. Sarah's got a bit of that going on, but you can't see it from your angle.
Harsh sun is pretty bad for portraits too. People squint (Roxanne), shades go on, and like you said - one minute they're in shadow, the next bright light. These are difficult conditions and the last thing you want to be doing is fiddling with settings. The EC dial is right under your thumb and Phil is on the money with... well... everything he said. I do think you did well with the exposures though. Only Rosa is noticeably under.
I think if you have her attention, do it! But avoid (for example) harsh sunny days where she'll be squinting and you'll have the sun sending your meter all over the show. You'll end up with (I suspect) much better images. Don't get me wrong, I like audience-gig style photos, but I'm not getting much emotion through in these. But it's early days. Keep plugging away. Once you get to know your camera, you can concentrate on getting the picture. I think you're well on the way to nailing exposure (well done for sharp images wide open too!) it's just the creative angle.
Practise practise practise!!!
Edit to add: Have a look at some of Mick Rock's work, or (less famously) Kevin Cummins. Both have some super live gig images as well as "rockstar portraits".