They were in pristine condition because the CGI tech to make the ship constantly damaged every episode didn't exist back then on a TV budget, that's why by ENT they could do that kind of storyline: The cheap CGI existed.
Also, they shot themselves in the foot with their "No Support" part of the premise.
"No Support" means that they'll never make any friends, they'll never trade or find repair stations, they'll never be able to create a power base for themselves, they'll never be able to get involved with local politics, it just means they'll be flying through everything and never get involved.
So basically, you've lost nearly half of the dramatic and creative potential thanks to the constraints of a the premise.
Also, knowing how to get back to the Alpha Quadrant also undercut a lot of the potential as well.