Unless you are an obsessional person like myself who is prepared to get under one of these things with a dremel and cut out every patch of rust, i wouldnt touch one with someone else 10 ft barge pole.
They are a minefield bodywork wise. Even so called 4k+ cars will have extensive rust in the hidden places such as the area around the aux fuel tank, jacking points and lots of the underneath seams.
Many people own a williams without actually knowing how good they are because they are driving a car with 10 year old rubber parts on it. I drove one 'enthusiasts' car once at a meet and there was 1 cm or so play in the steering column he was unaware was not meant to be there.
Unless you change all the bushes and mounts at the same time, you never get a feel for how good they are.
Buying a 1700 williams will give you an impression of how a worn out williams will handle.
So what is the point?
And dont bother with anything that has been modified with poly bush crap or runs the wrong 195 tyres. It will drive like a bag of nails, whatever the previous owner tells you.
Having said that, a standard williams in good condition on the right road (witht he right tyres 185's only please) is an amazing experinece, which i have never seen properly recreated in any other renault clio.