I don't have the money to buy many games.... but then I very rarely sell them, and as such I play most of them to death.... usually "completing" (the definition of which changes between games of course) them 3 or 4 times.
If you divide my game collection by the total number of months I have been gaming (approx 13 years = 156 months... probably a little more than that so I will say 160 months)
Then including VC and Wiiware I get 1 game every 2 months. or 0.5 per month.
I have only bought 1 game "twice" using Virtual Console so I should probably not discount VC games.
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Since I bought my Wii 26 months ago though I have bought 30 games in total (10 VC and 1 GameCube).
So in that time I bought more than 1 game per month on average.
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The number of games that have been sold is all of the Megadrive ones (I think I had 2 more than stated in my collection, but for this purpose I will just say 9) 10 of my N64 games, and 4 of my GameCube games.