I bought my first mk1 frs 3yr ago with no service history, average condition, bit of rust on the rear arches and 90k on the clock. I sold it in March for £800 more than I paid for it and it was showing 120k. The seats were in poor condition with badly torn alcantara, other than that it was a tidy car. In the 3yrs I had it I spent around 1k on it and that involved having the arches painted and modding it from standard to 300bhp. There is definately money to be made with them if you buy the right car.
When I bought mine I still had my saff cossie and after couple of years I had no use for the saff as the focus was so good at doing everything! I sold the saff but 6 months later then sold the focus too and bought an escort cossie. That only lasted 8-9weeks before I traded it for another mk1 focus rs. I'd never own another cossie again now! In my opinion the mk1 frs is one of the most underrated rs's. My new one is around 340bhp and would destroy my old 400bhp saff and escos round any track or on the open road.