I've you've just gotten into home recording: no. If you've checked Cubase 2 and know most (and I really mean most) functions it has, then yes. Cubase 3 has many more functions that make stuff easier. Not that they can't be done in other ways, just not that easy.
Can i have the link of a site that sells Cubase SX2 for £15?
I could then buy 33.333333333333333333333333333333333 copies of it for the same price as SX3 and put one on very computer own for no reason apart from the fact that i can.
Now all i need is 33.333333333333333333333333333333333 computers......hmm...