I don't think it's ever going to be a special, original car that collectors are going to want to pay a premium for, even if you put it back to standard. I wouldn't make any modifications from how it is now for the sake of increasing its value. The only reason to change it is to make it how you want it. If you bought it as an investment or to try to make some money, I'm afraid I think you should have held out for a more original car to start with.
Even a mint condition, 1 or 2 owners, low mileage, entirely original mk2 Scirocco is going to struggle to make more than £3.5 - £4k at the moment. Values have firmed up a little in recent years, but not quickly and even mk1s aren't worth half the value of an equivalent mk1 Golf (despite arguably being better looking, a better driver's car, and rarer).
Register Member 829
1980 Mk1 GLi
1980 (1976) Mk1 Junior Cup Replica
1982 Mk1 GTI (pending project)
1987 MK2 GTX