IMO, take them off and let a shop sand, scuff, prime, paint and clear (seal) them as they will last longer in the long run. Although you can paint and use them, eventually you will find yourself painting them again later down the road.

 

Yea i can testify to spending tons of money redoing spray can paint....I spent $25 twice for spray can match paint and $25 in match poly paint could do two grilles