What are your intentions for it, general bashing about or racing? The Durga is capable of both. The recommendations below are fairly general, and aimed at reducing your long-term expense, with the side effect of increasing performance!
Instead of buying a 6-cell NiMh battery, I'd suggest you get a Lithium-based battery - you'll get a lot more runs out of it, and the charger appropriate to it won't be obsolete shortly (NiMh batteries are probably on borrowed time). A hard case Lipo costs a bit more than a NiMh, but you'll only need the one for a long time. You could also use a LiFePO4 type battery like
this; they're excellent for bashing, as they don't have the safety concerns LiPos do if abused.
The same may go for the Electronic Speed Controller - you may be better off getting one capable of running brushless motors (there are some that run both brushed motors, like the included 540 with the Durga, and brushless) - again, brushless require less maintenance, perform better and last longer provided you don't overheat them.
Lastly, I've seen on these forums and elsewhere that a slipper clutch upgrade is a good idea for the Durga. I can't comment on this, perhaps a Durga driver could?