I got the 21" Inscription wheels. I just think they are really great looking wheels -- very classy/elegant and fits the overall luxury stylings of the Inscription perfectly.
I have them on the spring suspension and am quite happy with the ride. 20s may have been a bit softer / absorb bumps better, but I'm more than satisfied with how my vehicle rides. No complaints.
As you noted, you might pay an extra $100 per tire or so, but especially if you're going to get a different set of winter wheels/tires, you'll probably only be spending this incremental amount once every 4-5 years. I'm not trying to downplay the price difference as it is real money, but we are also talking about buying a luxury car and then paying up for the most expensive trim level they offer, so the extra $750 for the 21" wheels and the extra $400 or so every 4-5 years should be considered within that context.
