Re: Looking for a new camera
I'd go with a Canon, I've been impressed with their high ISO performance/low lighting.
Also, look into their IS (image stabilization) lenses for your low light needs, but as these lenses are expensive, you'll probably have to wait a while.
The Canon would be a good place to start. Good luck.
PS: my personal experience says to avoid panasonic, might just be me though.
Re: Looking for a new camera
If I'm not mistaken Canon has the largest range of lenses(60+ lenses) which will fit on their current lens mount system. While good, I'm not sure how much longer the EF format will last as it is over 10 years old.
I would also say Canon imo. Its a wonderful company and like Mr. Yuck said, they have very good images in the high ISO range, which would fit your needs perfectly. A good IS lens that I love to bits is listed in my signature. 28-135mm F/3.5-5.6 IS. You cant go wrong for the price, and you can usually find an excellent quality one on eBay for $300~
I would save for a 350D or 300D and get a 50mm F/1.8 lens. It only costs $75 or so, and is EXCELLENT on low light situations. You said you have a good distance from the stage. While in the crowd, the small camera and lens will be easy to handle, and the lens will become an 80mm~ lens on the 300/350D. Should be a nice reach to the stage if you're close. ISO 400 + a 50mm F/1.8 in that room setting with the stage lights should give you a shutter speed of 1/60th - 1/90th.
Re: Looking for a new camera
The problem is you will need FAST lenses. Most SLRs do have fast lens Like the Nikon F1.2 if you can find it or the Canon or Nikon F1.4. The fast lenses are mostly 50-55mm lenses and that works out to about 75mm (in most Digital SLR's) very good for portraits and low light photography.