A little though, hi res skins downloads could be upgraded to 2048x2048 and normals would be 1024x1024. I can't see 1024 to be hi resolution in any matters.

A big +1.

The problem would be that this means 4 times file size, but technology has improved a bit since LFSW was built

+1.

Joining onto full servers are going to take ages for some people though. (4x larger skin file and 30+ cars on track...). And I'd guess the cost for downloading hi-res skins would go up as well.