Well you might not want to wait too long, Last Story and Xenoblade are still holding their current prices pretty darn well considering their age. It's just conjecture, but I would guess that since they both had pretty small print runs as well they may be pricier titles in the future since they came out near the end of the Wii's life.
Oddly enough, I got an email from GameStop a couple of months ago telling me to trade in Xenoblade since the trade in value on it went up. I just chuckled at the whole thing.