depends, a car is worth what someone will pay for it. if you buy a cat D, then when you come to sell a car, someone else will buy it if its cheap enough.
Also, in my opinion, if a car is declared cat D at 20k miles, and then goes on to do another 80k miles afterwards, it really isn't that different to a HPI clear car that's done the same miles. I'd say the cat D status loses impact over the years.
Personally, I would make yourself known to the seller and let him know you're interested - with 2 days to go and no bids, it might not get any bids at all, in which case you could offer 7.5k or something ludicrous, see what he says.
And besides, if you want a 370z, then buy it, and worry about resale value in 4 years time, after having enjoyed whats probably a perfectly serviceable 370z