This is something I have huge problems with. I want to build stuff just because it looks fun to drive, but then only have limited cash for the running gear. So I think well if I'm gonna build something it has to be something that looks like it stands half a chance as it's the only robot I'll be building for the next few months etc.

Like Dave says (good name that) a lot of the wedge shapes and angled armor are highly used because they work well, the same with CO2 and spinners and invert-able chassis. All the robots are going to have to compete in a similar environment, so everyone's building to defend against similar weaponry and so on. If your looking for some inspiration, look at Craig Colias' threads and Google Mark Setrakian and some of his robots.