it is an enthusiast forum.
I have seen 3/4 very low mile one owner g40s (and owned 2 myself). One of a friends was factory fresh with 32,000 miles (ish) went for about £3800 and one of mine with just 50,000 miles went for just over £3000. These were in less financially harsh times too.
Both were standard, had service history (including cambelt service, new plugs, leads, exhausts, bill of sale etc)
This is the basis of some of the comments.
Good luck with the sale, I'm sure its a very nice car. However rarity doesn't often mean desiribility and if it was a mk2 golf gti 16v, i'd probably agree with the valuation.