You should NOT use wet performance unless the runway is wet. Damp is not wet.
I disagree. Unless your FCOM or other formal procedures require you to use "Dry" data, use "Wet" data (with "Good" braking action, unless otherwise reported) if "Damp" is not an option in your performance tables/computers.
AFAIK, the US FAA still does not recognize or use the term "Damp" (as of SAFO 06012 re Landing Performance Assessments, still valid as of AC 91-79A of 17 Sep 14).
A damp runway is NOT dry, so you CANNOT assume that there is no degradation of braking performance. Further, you cannot dynamically assess the current status of a runway's grooving or porous surface, so you cannot be assured it retains all the characteristics for which it was designed. Further, the old 'wisdom' of accepting a wet, grooved runway as equivalent to a dry runway has been addressed and challenged in several presentations over the years (I'll try to find and post the references if nobody else chimes in). The potential degradation in braking performance for a worn, grooved or friction-enhanced-surface runway has been more recently assessed as high as 30%, which is well above previous 10% estimates AND above the 15% margin used in performance calculations.