NO
Definitely not needed. It does boost the HP a bunch, but as for duning I can't see how it would help too much. In my opinion, turbo's on these things are just for the hill. I think they hurt the reliabiliy of the engine and trans. My car is PLENTY fast up the hill and def. through the dunes. You'd be amazed the power the Busa makes stock. It's much more torquey than I expected. If you like hill shooting, get the turbo. If you like duning and occasional hill shooting don't waste your $$. BTW, I have beat quite a few full size LS1, LS6, etc cars over at the hill even w/o a turbo.
Any manufacturer can usually custom make your car to fit your needs. Josey from Sick Sand Travel just built a car for a guy that was 6" wider, taller, and maybe even a bit longer too. These cars are pretty roomy considering their size though. Sanddunesaddict (Bert) is almost your size and he drives my car with no problem. If you want to stop by my camp this weekend, you can check my car out and sit in it to get a feel for how big they are.