I'm back in the hobby after a 2 years pause... I have a Spektrum DX2 that I used with my RC18B. Now I'm thinking about an 1/8th Electric buggy, will the range of this system be enough?

Is there a sensible difference between my old and basic 2.4GHz and the new Futaba FASST and Spektrums ?

The DX2 will be fine and I doubt you would notice any difference between that and the newer "faster" systems out there.

dx2 is great cost efficient. You will not have any problems using it in a 1/8th.