Value depends on mileage and condition now, more than age.
Mods can add/subtract value depending on what they are / how desirable they are.
If your car is sub-75k miles, then potentially £45-55k depending on how much proactive maintenance you've had done on it / how much needs to be done. If sub-50k miles then probably top-end of that range.
If your car is +/-100k miles, then arguably £40-50k, only top-end if it's absolutely pristine.
All that assuming a manual car that's not Cat-D, and there's little in the way of mods other than the facelift.
...and that's based on a review of advertised prices (mildly adjusted where someone's obviously chancing it), NOT necessarily sold prices, of course...
PS - always found ClassicLine to be good to deal with. Never had to claim though...
"No man with a good car needs to be justified"
Blue '08 FD2 CTR - big, ITR-sized shoes to fill...
Yellow '96 NSX 3.0 - oh was it worth the wait!
Black '99 ITR - well, I had to have another one, the first was so much fun. Miss this one even more than #1...
Blue '03 S2000 - SOLD, flawed but fun
Blue '04 Focus TDCi Sport - SOLD, very good fun for a diesel!
Black '00 ITR - SOLD, still missed
Red '98 Civic VTi - SOLD, probably still bombproof