I was at solo nationals and talked to a couple of the mini drivers. There were multiple r53s and r56s. They all found ready made skid plates that also protected the bottom of the radiator. They had custom guards around the rear lower shock mounts. That bolt is holding the rear suspension together and they didn't want a rock strike to lead to a completely collapsed suspension. The r53 guys looked like they had problems keeping their rear bumpers on.

An 05-06 r53 with the short 2nd gear would make a fun car in stock or prepared. You get a linear throttle response and the right amount of torque to avoid spinning tires all the time. I bet a turbo car would be faster on a low speed course though.