You know, I'm the last person to ever say this, but this has been discussed a thousand times in the various threads, and there are official threads for these panels, and an official thread for the entire line.
With that said, I'll try to answer your questions as best as I can.
A while back and hdguru article arose with Panasonic claiming the GT30 will have a black level of .004, and the VT30 with a black level of .002. In the same article, they mentioned they've gotten rid of floating and rising blacks.
We don't have enough information yet, but so far, floating blacks are 100% gone, and depending who measured it, the GT30 is around .004 black level, meaning it's pretty safe to bank on the VT30 have .002, or damned close to it. And obviously, black level means better contrast, and so forth, and a better picture overall.
It also has a 10 point gamma control, so if you get it calibrated, gamma will (hopefully) be very close to perfect, but that's all speculation on my part as the VT30 doesn't come out for a bit.
The increase in black level, the overall look of the panel, + 96hz for 24/p content makes the jump completely worth it, but that's because I want the best possible picture quality. The GT30 is an excellent panel though.
Hope this helps,