You may get it for £9k, possibly less.
Seems a reasonable price to me?
If I was in the market for a later model classic within that budget I would give it serious consideration.
A cynic knows the price of everything and the value of nothing as Oscar Wilde said.
The value in these type of cars comes from the originality and superior condition.
One owner, low mileage, original paint, never welded and rust free.
Those five factors put any classic model of any type in it's respective higher price bracket.
I would always pay the premium over a standard/average example that may be bought for a bit less money but may have had multiple owners, a bit of welding and paint here and there, higher mileage, tatty interior etc etc
The more angular shapes of the late 80's onwards are becoming more fashionable again so maybe now is the time for the Z31 to step forward. Funny how there seems to be a real bias against the N/A cars compared to the Turbo cars amongst Z31 owners.