If you really want to ad some pizazzz, polished covers are the way to go!
Start with 120 grit wet and dry sand paper wrapped around a flat piece of wood (so you don't get hills and valleys). Be sure to rinse the paper often so it doesn't load up. Once you get past all the dimples and casting deformities reduce grit to 220, then 320 untill you get all the deep scratchs out. Then a buffing wheel with buffing compound (I use white diamond, cuts almost as fast as Tripoli but leaves it with a finish shine).
If you don't have access to a buffing wheel, with ALOT more work you can reduce sanding paper to 400, then 600. Rubbing compound with LOTS and LOTS and LOTS of elbow grease will give you the finish shine.