you cant see 600 grit scratches when painted. if you dont sand, that half ass paint job wont last a year. the only thing holding it on will be the clear. and when you get a rock chip it will start flaking off. then you will have to re-do it. and sanding doesnt take that much effort and time. do it right the first time.
Plastic does not need sanding. soap and water, air dry, clean with cleaning solvent, adhesive promoter, then paint and clear. And sorry, that does not constitute a "half ass paint job (that) won