New cars depreciate. It's pretty clear looking at 2-3 year old cars and 10 year old cars there is a gap in values. Not sure it should be such a big factor in owning this sort of car, but that's a different discussion.
A newer car is no guarantee of reliability, arguably the opposite in fact. Modern engines are much more complex than Zetecs, Red Tops, etc. It's more about the builder - someone who has had the car a few years and ironed out the issues will provide a much better car than someone who liked the idea of building one but had no mechanical knowledge, learned on the job, got it through IVA then sold it.
Spend c.£10k on something 10+ years old and you can get something that will hold value if you buy smartly.
IMO best way is to treat them like you are riding a bike. Keep yourself dry with good clothing, drill holes in the seats and floor pan to let water out. You won't stop it coming in successfully, without having steaming up issues, visibility reduction and flappy hood syndrome. If you want all this it's time to look at an MX5.