Well, thanks everyone. As she can't really do without the car (she hates the 164 because it's too heavy for her (and I feel happier when she's not driving it anyway!) we've decided to bite the bullet and get a new one from the Stealer - a mere £200 and he should have it tomorrow morning! At least the damaged rim was the skankiest on the car with half a ton of lead balance weights already on it, so we'll have a decent set. I might well still look out for a set of 16" wheels in any case though. The roads round here (rural Cumbria) are pretty lousy, so I think this is going to happen again some day. 16 inchers with 60 profile tyres might just cushion the rims from the worst that the road surface has to offer. I might even be able to sell the 17 inchers on Ebay!
Back to this tale of woe, however, I now find that during this "encounter" there seems to have been some damage to the flexible hose in the exhaust and it's blowing. (OH, and there's rather a lot of grass on the bottom of the car)! I think I can feel an exhaust parts post coming on...!