I have been collecting for a late 1940s to early 1950s film noir vehicle set, simply because they are easier to find.
Also some 1960s stuff for spy gaming, and contemporary military, emergency, and police vehicles for...I'm not sure yet.
Mostly Disney 1/50 'cars' with the eyes painted out, and M2 1/64 Cars (the larger ones look okay; nice trucks), Tonka strike force, a couple of batmobiles....