Even if prices soften from £45k ... which will be dependant upon how many of the 150 want to flip or have been bought by the trade ?!! But given that only 4 cars are presently for sale, all at £45k it looks like cars will be in short supply ... even if prices fall, which I am sure they will, it's still a very strong % return on your investment.
Regarding VW building more CS-S cars that simply won't happen - it would leave any further limited car runs in contempt and devalue VW's honesty and integrity even further after the diesel emission scandal. Also, the mark 7 is up for a replacement so the sheer practicality of the manuafacture process would render the idea futile.
As a GT4 owner, I think the CS-S to follow a similar pattern and in a years time be valued around 10-20% over list price. However there has been well over 400 GT4's produced for the uk so the 150 CS-S cars will,be in even shorter supply and at a lower price point.
We live in an age and time where anything and everything is considered collectible - the RS market is very strong, even MIni cooper works cars are appreciating in value. House prices are relatively frozen, interest rates all time low. So people look to use there savings to purchase "investments" driving the classic car market and having a knock on effect on any limited run car - be it Focus RS, M2 & CS-S add to that Nurburgring record, runner up in ECOTY to 911R, finalist on Chris Harris Top Gear car of the year and you have inflated prices that will stay that way until the classsic car market softens or until interest rates rise or house prices start to increase ... Wine is also currently a good market for investment - I tried that but kept drinking the profits .... haha