FWIW, all my shots are on a 30d, and they are plenty acceptable concert photos (IMO). Point taken on the blow up factor for film and full frame though, and the wide angle of full frame, but you can do just fine with a 30d/40d. In fact, I'd argue the glass is probably more important -- I use some pretty nice glass, and it pays off. That said, I'm in the market to go 5d, thinking about waiting to see if a 5d Mark II ever comes to fruition in the near future, and if/when it does, I'm going to make a play for a used original 5d.
BTW, I just made a pretty nice audio slideshow merging my audience recording with photography that I'm kind of proud of. Not perfect, but getting better. Check my sig for samples...