I just got a blitz and upgraded to the CC 4600kv brushless. I am curently running nimh 3600 and run times are about 10 or 11 mins. What will I gain by going lipo? Power, speed, or run time. Is it worth buying a new charger and new batteries?

Yes, yes and yes. I have 4000mah lipos and get 15 to 20 minute run times weth excellent power and speed. Long term it will likely be cheaper to run lipos as they have a longer life than NIMH.

The lipo's are a fair bit lighter as well, so that should help acceleration.

Well I got my bantom charger and now just waiting for the lhs to get lipo's in stock.

You should feel much more punch on throttle. The lipo's can discharge faster than the NiMH thus getting more power to the motor.