I'm surprised there's no other response, as there are much more knowledgeable people that me here. I have no experience with concerts, but I do have experience with indoor sports, where there are similar problems, and poor lighting.
Yes, you will increase contrast by pushing- I think of it this way, what you're really doing is underexposing the film, then giving it extra development to compensate, so that underexposed negative will have poor contrast, and your extra development is making it more "normal." Wherever you're placing the performers face, at middle grey, or whatever you're envisioning, the amount of highlight detail you'll get above that will be limited by the film stock, the development procedure, and the scanning, as it sounds like that's what's going on- you don't really know where the limiting factor here is without carefully examining the negatives and controlling for some of the factors, but when using a lab to develop, your options are limited. You might have to adjust what you're doing to the results the lab can provide (e.g. expose for highlights) if you're stuck with that one lab.
Remember too that the "box speed" of films like Tmax 3200 already reflects a push- tmax is actually an ISO 800 film without any push, so when pushing to 6400, you're essentially pushing that film 3 stops rather than one.
In your shoes, my first thought would be- can I get away with flash? Tmax 400 either rated box or pushed one stop with flash would let you negate some of the uneven lighting and highlight issues by adding your own, even light. Otherwise, spot metering for what you want as the most important aspect (faces, it sounds like), using an incident meter on the stage itself, or just trial and error would all be helpful. Faster lenses are your friend- every additional stop is twice the light, and twice the shutter speed.