With a crappy mouse, the mouse pad doesn't change much in the way of mouse performance. One benefit to the nicer mouse pad is the comfort it provides to your arm whilst moving across it. My old mouse pad felt silky and cheap and had a lot of dead spots where the mouse rubbed against the loose fabric and moved the fabric with it so I couldn't get movement out. Now this doesn't mean go out and buy a corsair or razer mouse pad; I'm a massive corsair fan and even I think those are a waste of money. Glorious and Steelseries both make some excellent mouse pads and a cheaper mouse from a reputable brand isn't a bad idea either. It really depends on how bad you hate it.
Just a few mouse pad suggestions... (I'm only providing amazon links...