I got my PS3 about a year and a half ago and a lot of the games that I got early on were cheap or on sale during Black Friday. But last summer, I spent about $200-$300 on games that I finished pretty quickly and Platinumed in less than a week, like inFamous 2, LA Noire, and some of the Lego games. That's when I decided to get a Gamefly account instead because once I'm done with the trophies ,I feel like there's no reason to go back unless I'm bored one day, but with the amount of good games that came out last years, it was hard to find time.
With that said though, there are some games I would never sell because I like to think I have a collection of must haves. I have all three Uncharted games, Every Assassin's Creed game, both Arkham games, and I plan to buy Mass Effect 3 even though I already finished it as a rental. I haven't gotten all of the trophies in all of those games just yet, but even when I do, they're all just so good that I have to keep them. I would've kept both inFamous games, but I was really desperate for the money at the time and knew I could get a good deal since they were still fresh off the shelf at the time.