I would sell the sealed copy relatively soon, if you're really interested in the money to be made from it.
Demand for a sealed copy could pretty easily fall off. Anything could happen, sure, but this doesn't seem to be an Earthbound or an FF7 or a Valkyrie Profile where the game has a really strong fan following to drive the price up. It won't receive the followup that will make latecomers take notice and try to hunt down the first game in order to experience it. It also has an EU version that can be bought for cheap.
There are only a few games where years of holding out has really paid off in a big way. Based on the prices being paid now and the factors mentioned above, I seriously doubt it would be worth waiting "years" to sell it for an additional $30, or even $50. You could have bought other games or done other things with that money in the meantime.
Just keep the opportunity cost in mind, whatever you decide.