The buyer's market would increase for planes that are not LSA-compliant, but would fit within the new sans-medical guidelines. This would serve to increase their value and prices. Saying "I know some guys and they aren't interested in a 172" is nice, but not scientific nor a large enough sample to matter. Additionally, as there is no requirement for any aircraft to equip itself with a WAAS GPS or EFIS, I'm not sure where Bill is getting his information on keeping aircraft legal and airworthy.
Cost of used 172 + ADS-B Out < Cost of new CTLS
Capability of used 172 > New CTLS