Not an investment at all, it's only a Focus RS.

When you take into account that you could put £10k in a decent savings plan and leave it there for 10 years it will yield a much higher return and command far less maintenance, all you would have is some minor admin as opposed to storage and maintenance considerations and associated costs like insurance or overheads, so whatever you think you'd made on the car, it will be largely eroded by what it has actually cost you to keep, even if you never drove it.

Also, if we all take our Ford blinkers off for a second and someone said buy an Astra VXR as an investment, you'd probably laugh, just because its not a Ford, but what is the difference?

Yes there are some success stories out there, but they don't apply to the modern RS range and never will to the same extent as days gone by IMO