I think that if that car, being a very late Plus is as good as you make it out, and looks in the pics, you should hold out and wait for the best offer, if it's not good enough, then keep it.
Coop prices may be low, but I've noticed the asking price for coops on AT, PH etc starting to creep up again. "Special" coops rarely appear for sale and if someone wants a really, really good example, they should expect to have to pay for it, I would expect to pay over the odds for a pristine example of any potentially special/classic car and from here at least, yours looks like a superb example.
IMHO of course!
Gareth