Hey,
Is a new cap and rotor really necessary or can I gentle clean off the cap and rotor tip with say 400 grit paper and electrical cleaner?

what ya say?

 

If you've gone through the trouble of removing the Opti then I'd recommend cap and rotor replacement. The brass contacts (both rotor and cap) do physically erode. A simple clean up may work for awhile but won't last.

 

Also I believe the contact points are coated originally, so sanding then wil only expose the metals and corrode quicker. Removing any contamination will only be a temporary fix and you'll be back in the same boat id guess in a year or less.