The problem maybe with the GTR and Alpine is that the are making decent numbers of both. Investment value is often linked to relative rarity which neither qualify for. I know I mentioned a couple of cars which may suffer the same fate upon reflection.
For example, there are only 1421 Porsche Cayman R worldwide which compares to over 40,000 Nissan GTRs. That's a massive difference. There are now over 12,000 Alpine A110s out there and counting.
There are 1911 Aston V8 Vantage S coupes and 825 roadsters. Low numbers. For Mr
@Felonious Crud there are 1277 V12 Vantage S coupes and 363 roadsters, oddly they made less on the non-S versions.
There are 9195 Alfa 4c variants out there.
So, to summarise, with 45k or so to spend, I think I'd buy a Cayman R. It's the first aggresive Cayman and so has a place in a significant market of Porsche enthusiasts. A much bigger market than almost all other brands. Supply vs Demand.