I work at a dealership in Upstate NY. The preowned WRX market is very slim. We get one or two in a month and we're one of the largest dealerships for quite some time. Honestly in most circumstances it's hard to justify buying preowned when you can get a new base for $500 more, but it really depends on the car and situation. You need to remember, if you were the guy that traded it in you would want top dollar, and we're faced with balancing keeping customers happy on their trade, customers happy with their purchase on the other end, and making some kind of profit. Preowned WRX's are definitely a tough market.
I'm still stuck in the land of 02-07, my heart will always lie back in that era. Still overpriced for the years, and finding low mileage is tough if that's something you care about, but in my opinion it's the way to go.