Star Trek is a product of its time and IMO holds its own compared to other late '60s shows. The older it gets the less it will appeal to a broad audience, just like any other show. Some people will still appreciate it, either for historical value or because they like its "vintage" aesthetic or production values. But they will be a small, specialized niche audience.
I agree with this. Having just recorded 36 episodes of a podcast whose purpose is to discuss TOS with a non-Trekkie, I can tell you that even for people that like science fiction, TOS is a hard sell.