I think the other thing to consider is that the reason why we get a game at the time changes, and so do we. I went through many phases with gaming, considering at one point I wanted to play nothing but Zelda, and at another time, I wanted nothing but Half Life, etc.
I guess the key is to ensure that you are fine with spending the money on the RIGHT to play the game, as opposed to wanting to definitely play the game. I never value games by the hours/dollars ratio, as I feel that valuation in general fails. There are so many things I can do for free that are funner than gaming...gaming is for certain moods, and certain times. It's not a "I spend $20 to see a movie, so my entertainment budget is $10/hour" or other such rubbish.
I just wish sites like GOG and Steam would allow sell-backs in some form. For GOG of course it would be for undownloaded titles only. I thought of a system once before, where Steam could allow you to trade back previously purchased titles for UP TO their profit margin towards another game, with a maximum trade-in.
For example, maybe Steam makes 50% off a given game, let's say Call of Duty 4. Now, I have played this out, and I hate seeing it in my list, bloating things up, and doing noone any good. So maybe Steam sells it for $20 now. SO they allow me to trade it in for up to $10 off another Steam game. Obviously, they would need to allow users to trade more than one game towards another, while still ensuring the publisher gets their cut. But I feel this could be implemented in a way that would allow users to perform a "Buyer's Remorse Erasure".
So I suppose, the way I deal with a backlog is to recognize that I don't necessarily have one, as I probably have no intention of playing many of the games I have bought.