In case you missed it, I posted a link to this review a few days ago
It seems to concur with what you've heard - the Clio III 197 is a better built car than the II 182, but isn't as quick or as much fun to drive, largely thanks to being that much heavier.
As for repairs, my limited experience suggests that it'll cost you less to trade the car in 'as is.' I suspect that the dealers hang onto them until things are slow at their bodyshops, and then effectively get them repaired free of charge apart from materials. The damage will lower the trade-in value a bit, but you won't make your money back on having the damage repaired.
We got a reasoanble deal trading in our 02 Clio against an 04 (we needed a 5 door.) To be honest, I think they gave us a bit over the odds on the trade-in, but charged a bit over the odds for the new car. But 3 grand got us the same spec with the extra doors and less than half the age. I'm not complaining. We actually saw Leo (the wife's old Clio) today. The first time since we traded 'him' in
Selling privately might be a completely different kettle of fish. Most people want something that doesn't require any work, so unsightly damage is likely to put off the punters and significantly lower the price that you eventually get. If the damage is limited to the bumper, then phone round a few scrappies on the offchance that you can get a same coloured bumper from a write-off with no rear end damage.