Peter I feel your pain and your observations are correct.
In my mind a descent GranSport with mid to late 30's on the clock in LE guise is worth £24k, maybe a grand more for an exemplerary model. The issue is that 9/10 cars have fallen into the trades hands so very few private examples come up.
When they do, they are loaded by £3 or £5k
Last summer you would have to wait no longer than 3 or 4 weeks to find a descent private example, but of late, and at the lowest point of the year, a couple of GS's have come to light and stupid money. Then anyone else wanting to sell their car look at the ones for sale and again over value their car.
What should drive price is supply and demand, the supply is their but nobody is going to pay silly money for them, Hence cars are just hanging round for ages and until the current crop clear prices will remain inflated and the market stagnant.
Also the GS has this stupid 50k mile barrier thing, once they go over they become worthless.
As a case in point, a new member on here has just bought the grey with full tan leather GS from Simon Jordan in Bristol. It is in excellent condition and a great spec and colour combo, 49k miles and descent clutch. It's been for sale for 4 months and finally sold for we assume £22k. Simon has got a great car for the right money.
This car took 4 months to sell so what hope has someone with the same spec and mileage for nearly £30k.
I phoned up a private seller and offered £26k for an LE with 40k miles on the clock and he just laughed at me!
The markets gone made so I, like Peter and 3 others I know of simply will wait it out till the market corrects itself.
Rant over, back to strictly.... I love those flappy skirts!