Looks like a lovely machine. It has the usual "saggy ar*e" syndrome these all suffer from. I just did the springs and shocks on my 940 at the weekend and it makes the world of difference.
I don't think any of your negative points are even worth bargaining on. It's a 27 year old car after all. All of those points are more common than not.
Just one on the positives: if the timing belt was done at 80k miles, it's at least 17 years old
and about 12 years overdue. Still, I think it's worth £2750-£3000 of anybody's money.
Good luck with the sale.