Tough call, especially on a trade-in. There is a much bigger resale market for a CTS than there is for a V . But there are a lot of CTS's coming off lease. Dealers will look at how quickly they can move a trade-in, not necessarily at the original purchase value.
The used car market around here is saturated. So trade-in money is most likely suffering.
My thought would be that the V has such a specific market, that you could treat them as seperate vehicles, but you are at the mercy of the dealer to see things the same way.