Rolling C - I agree with you 100% on this!! I flew C150s with RR Continental years ago and was told by my instructors that the PA28 with a Lycoming engine was a totally different beast. Touch wood, I've never experienced carb icing in a PA28, but a poorly set up engine can suffer badly from the fouled plugs and over-richness which you describe. A response check/engine warm every 1000 ft in a prolonged glide - as for a PFL - is essential. But I've never bothered with anything more than a brief check of carb heat in the circuit - if conditions are so bad that a PA28 could suffer carb icing in the circuit, should you really be flying more than 1 circuit to land anyway??
RC - do you think one should bother with any 'final check' apart from 'Toes off, reds, blues, greens'?? I'd be interested in your opinion!!