Jeff,
Well, TimD is right on the money. Plus sizing with the same tire given a smaller sidewall height should improve steering response and could have less rollover therefore keeping more tread flat on the road. As for experiences, most people when bying new rims either buy bigger (for summer) or smaller (for winter). 215/45R17 looks perfect to me on a Contour. Money aside, I'd go for 17's with Bridgstone Potenza RE730.
However, even if rims are not much more in 17 vs 16, tires almost always are. Up to $25 per tire and that's and extra $100 every 2-3 years. Don't know how much of a factor that is, just keeping you informed. I think either route you go with a good summer only tire like the KDW or RE730, you're going to speeding up for every turn.
As for rubing, 215 should be fine as many have 225s. When you order at Tirerack, talk to Luke and he'll make sure you get the right offset.
Aaron