When I first started building robots, the best advice I got was that the more successful teams have stuck with an idea and evolved it. I'm not a great builder, but my current two wheel drive pusher is about the 7th incarnation and quite easily stands up to most beetle spinners. Once you've competed for a while and seen a few events, you get a tangible feel somehow for the energy certain weapons carry in different weight classes. You can keep rebuilding and putting the robot in with nasty stuff till it comes out unscathed. At that point you'll find you start to get further in the competitions your attending n stuff.