I think the S1's are worth good money, if everything is original.
The ones down the lower end of the money range, like 2k to 3k are gonna have had panels replaced, maybe even some of the wrong parts on from say like an S2 etc.

The cars that are gonna fetch the money are ones with low miles, excellent history, original panels, original engine, gearbox etc.
A lot of S1's have been restored to as new spec, had concourse body rebuilds, using genuine panels and parts, these cars tend to command 5 to 7k.

As for the 7k miler, im sure its a beautifull car, but i don't think its worth as much as 17 grand.