That's mostly what I do with new games. Whenever there's an offer, I ask myself "Am I going to play this for at least one or two hours right now?" If the answer is no, then I don't buy it.
That's not the same for local cooplayer games, though I have way enough to fulfill two lifetimes, and recently we're just playing through the Wii catalog.
(I didn't want to be dismissive of this approach, I was just airing my grievances)