You can get similar aged Boxster S sub 40k for 12k upward. Caymans are still holding their value ok but less than the Zs now 16kish for a decent one.
Theres no arguing there OG but this is a recent case like I said 3-4 years ago they were rock bottom a 4 yo coupe could be had with sub 45k for 17.5k. Thats what I payed anyway. Milage and value most certainly did apply especially if its going to be an appreciating asset, I agree with you when looking at the coupe but not a roadster as its not a unique recipe and there are still NA roady competitors. The only Coupe competitor is the Cayman.
Struggle to find coupes with spec above now for 22k many cases more, just seen Knights have a coupe with 25k for 25k. The Coupe was always a strange one, the M3 was a better car in many ways and they were similar prices and the M3 ride was a lot better 2 more seats etc but wasn't a true sports car, but the M3 seemed a better purchase, so many coupes didn't sell and people that bought Z4Ms were a very specific unique buyers leaving the UK with 550ish total. People that wanted a sports car usually wanted a car that did more so they bought the roadster as roof down is selling feature, which is why twice as many were sold.
We are talking different cars with the CSL tho and the M3 evo. The evo started it all nostalgia for many and historic pedigree, the CSL was supposed to be a limited run the Z4M wasn't, It was just unpopular at the time.
As we've all said if BMW had made the E89 with the V8 it would have been a good seller and we would be having a different conversation.
I love the Z4M but after owning one and selling it for a good price I would need a lot more to buy one and I don't think I would be looking at another with current prices.