As much as we enjoy the Golfs, none of them have exactly out performed as investments.
e.g. If you bought a desirable 1983 Mk1 GTi Campaign, these were available new for <£7500.
If you adjust for inflation £7500 in 1983 is equivalent to £23,920 in today's money.
You would still have to service, mot a car for it to be worth anything today and there are not many immaculate Mk1 available for >£15k today.
For example if you perform the same calculation with some Ferrari, some air cooled 911 you could make a case for appreciation over inflation adjusted purchase price.
The closest car I can compare to the CS-S is the Audi A1 quattro of 2012.
Audi produced 333 of these (all lhd) with 19 coming to the UK at a cost of £41k.
4 years on and sub 10k miles cars come up rarely at low £30k's....maybe you would get your money back on an unused car that sat in a collection?
On that basis, I can see a CS-s holding it' money, but don't see it appreciating much, it won't be long before the next set of mega tyres reduces ring times on the next Ring spec hot hatch.