I love the earloves too. Their noise reduction rating is 12dB.
Foam earplugs actually have a higher NRR, but you have to wear them properly.
Here's a little bit about NRR.
http://www.coopersafety.com/noisereduction.aspxThis is part of what I do for my job!
But, I've found that the earloves work just fine for shows, and they filter out the crap so you can hear the show better. I don't think most shows would warrant a higher NRR (but I've also never taken a dosimeter or sound level meter to a show, either).
I would want a higher NRR for Mogwai or Fugazi though.