I suspect that you won the auction at a price that the car is worth, and if you had to spend £1000-£1500 getting it sorted you would probably break even in terms of car quality vs overall cost.
I think it was risky bidding on a car you haven't inspected, especially a car with the problematic reputation of the X1/9. But, in my opinion, you have ultimately made the right call in leaving the car alone. There is no way an honest seller would advertise a car without at the very least mentioning the speedo doesn't work - doesn't really inspire confidence.
I hope you find a more genuine example soon, but make sure it is soon - I am hoping to buy one in the not too distant future and I don't want any rival buyers getting in the way