As far as why a polish works on automotive paint is because it will sand down the clear coat and even it out. But it doesn't stop there, you need to coat it with wax and a good sealing glaze otherwise you will see swirl or stroke marks.
When used on a lexan body, it won't work too well. Remember, it will cut the body with the silica and there is no paint on that body to buff in order to hide the marks.
My suggestion is to just leave it as is, beat the body to death and buy/paint a new one when necessary. It's all part of the hobby. Bash,break,fix ... it's a vicious cycle!:marshall: