Hmm, I read somewhere that there was a very slight amount of 1.6's made in 3door, not sure on how correct this was as it was from this forum a couple of years ago...
Joe, Cat D is nothing to worry about as long as the work has been carried out properly, ask to see where it was damage and look for proof of the damage and proof that the work has been carried out properly, if you can't get an AA inspection done.
I'm not sure on how much the 1.6's sell for but 4k seems a bit expensive, check around and see what similar models are selling for, though generally Cat D will knock about 20% off the book price.
Cat D usually isn't very heavy damage at all, especially with slightly older cars, I had a Cat C car for about a year and you would never have known when driving it or checking where the damage was. (Which wasn't even that heavy in the first place)