The more I think about it, there's probably more value to video games than just fun and entertainment. Being so graphics intensive, with all the data, speed, interactiveness, they probably encourage an increase in computer capabilities. Memory, processing speed, etc. I see this as helping increase cheapness, through mass demand, for when you want to use it for scientific pursuits. The same would apply to co-operating with large networks of thousands of people, great for bioinform and other prediction methods like futurology, social trends.
Alternatively, such engines likely have alternative applications for military, like flight simulators, since games are more often coming up with complex physics engines to simulate reality better, I heard about this with Tribes 2. If you can come up with efficient engines for mass considerations of physics, it's only a matter of time until you could implement something similar to chemical interactions like bioinformatics. I always wondered how predictions might alter with full considerations of londom forces. Heck, you might even be able to include quantum tendencies in considerations for better accuracy, like they do with satellites and computer chips.
Even just considering fun and entertainment though, I believe they make you smarter, increase online social skills (if you approach it correctly), increase certain areas of finger-eye coordination, thought speed, strategy, reaction, and in general, enjoyment makes you happy, releasing the pleasant chemicals which um... cure stress?
