It is pretty nice, it has a lot of original parts under the hood. I bet that radiator is 1987 vintage. I guess it is pretty clean too, but mine was that clean after I detailed it. My wheel well is still cleaner and I drive mine everyday!
I would say $10k-$14k would be a fair price.
For $18k you could buy a 2001 XJ8 with 60k miles on it, cars don't hold their value these days.
It would have to be a weekend toy driving it everyday would be stupid. And you could never sell it because the value is only going to go down.