Thanks for your insight. It appears that prices of used SUVs already are skidding. The region of the country and the specific SUV make a big difference in how soft the price is. I doubt you'd get hurt waiting, and would bet you'd come out better on the price. In fact, the longer you can hold out, the lower the prices are likely to be for just the reason you mention.
Nothing's really comparable.
You can get the supercharged engine in the Buick Park Avenue, and that's a very pleasant package. It is, though, a four-door sedan and therefore not like Riviera. My favorite coupe just now is the Acura CL, but it's like Riviera only vaguely, in concept, so might not suit your taste. If you're stuck on coupes, you might have to check out the foreign brands for something suitable. I can't think of anything quite as distinctive and purely American as Riviera that's still on sale.