Cant really talk for the 172s, but if the build quality and general mechanics of the phase 1s are anything to go off then I wouldnt buy another one. I currently drive a phase one 16 valve, and yes it is a quick car, the power boost that comes in around 4000 rpm is great fun. It handles well, and looks quite aggresive with the flared arches and bonnet scoop. It is a great car to drive when it works. However, it is always going wrong. I bought the car with fairly low miles, a full service history, and every receipt for anything ever done to the car. I would have thought this pointed towards reliability. I have owned the car for 4 months and it has had:
new starter motor, new alternator, new front pads, new rear pads, new rear discs, new rear calipers, plugs, leads, dizzy cap, idle potentiometer, air control valve, power steering pump, wheel bearings.
The car currently needs: new clutch, new gearbox, new heater matrix, new ecu and some serious acoustic damping in the vehicle to sort all the rattles and squeaks.
When i bought the car i checked it over as best I could. The clutch was fine, the gearbox smooth and precise etc. Everything points towards poor engineering from Renault.
Now I know this site is devoted to Clio enthusiasts, and I too love my car. It is the best hot hatch I have ever driven (with the exception of a mates audi s3) and I will be sorry to see it go, but I cant be arsed spending and spending on a car that continues to be unreliable. The Clio is a great car when it works, and if the Clio ever met BMW or Audi down a dark alley, you would have one hell of a car.