I own 3 VC titles. Mario 64 (because I never played it), Gunstar Heroes (because I still play it), and Sonic.
The only purchase that I somewhat regret is sonic. That one I have played to death, and I bought purely based on nostalgia - which would have been fine if the price had been better.
Really to me, what it boils down to is price. Is a NES game still really worth $4-5, and a SNES/GENNY game $8? That's pretty questionnable. The price would be right for nostalgia if the games were half as expensive.
Overall, I think that the XBLA service is better. It does have retro games (although they don't have the same quality), but they also have original content, all of which you can try before you buy, so that at least the nostalgia can wear on before you make the purchase.
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