You need a buffing wheel to REALLY polish polycarbonate. If it was made out of acrylic, then hand polishing is doable. However, pc requires the aid of a machine with polishing compound to get the scratches and knicks out of the lenses.

Regarding the glass vs. "cheap plastic" issue, I'd go with the plastic. Yes, glass is nice but I think it may be susceptable to cracking from rock impact while offroading. Polycarbonate really isn't "cheap" either. Although it's still plastic, it's the same stuff that bullet-proof windows are made of like the ones in some banks.