My 156 2.5 V6 is currently on 156K miles. By the time you get to this sort of mileage, lots of things will have been replaced more than once.
The most serious / expensive items to watch out for are the clutch, (probably already done or currently extremely heavy - mine packed up at 120K miles), the cambelt obviously and rust in the floorpan and on the leading edge of the roof, where the roof touches the windscreen.
Suspension bushes need to be changed quite regularly anyway, so I wouldn't worry too much about those. I regard them as disposable items these days. The radiator is likely to have been done already, but if not is probably about to fail.
Overall though, they are brilliant cars. If the clutch has been done and you can't find any major rust, I would pay up to £1500, but it depends how you feel about the car. Sometimes you see a car and just know you have to have it....