Personally I love over the knee boots. When worn well, they look amazingly cool and/or chic. They might not be on trend forever (what is?), but I doubt you'd ever look out of style in a pair like
Jimmy Choo's April leather thigh boots.
I think a particular boot's wearability over time depends on its style. Clean, classic lines in a rich neutral color (black, chocolate brown, cognac, etc.) will stand the test of time. I could see wearing those Choos for years. A trendier style like these
suede wedge thigh boots by Rick Owen? Not so much.