Silver is the most reflective surface used for replating automobile headlight and signal light reflectors, even better than aluminum:
Reflectance Comparison
Silver: .95512 = 100%
Aluminum: .91320 = 95.6%
Chrome: .60604 = 63.5%
Source:
Refractive Index
The process involves taking the substrate down to bare metal followed by copper plating and then silver plating. The result is outstanding. the best way to go at this time.
Note: Price listed is for one typical 7" reflector. This service is available for reflectors from many marques, not just Porsches.