This is the later on down the road, and now would be the time to cash out. As soon as Sony makes a non-backwards-compatable Playstation, you're out of all your playable collector value. You may be able to market it to someone that wants to watch it build up dust on a shelf, but selling out now probably isn't a bad idea.

PS2 games don't need very many sales at all to qualify for GH status - the actual number is something like 200,000, which is usually easily achieved. The game's publisher generally decides to make the game a GH game when the sales figures are slowing down at a fast enough rate in which a price drop will significantly increase sales. However, this will happen if and only if the company decides not to discontinue the game despite sales figures after a certain time in order to preserve the game's rarity and keep the per-game profit margin high - Atlus is notorious for doing this, but Square-Enix isn't.

For example, FF X qualified for GH status in its opening week of sales rather easily, but it didn't become a GH game until almost two years after its release, because sales remained strong for that long and Square decided not to reissue a GH release until they thought that the significant mandatory price drop would benefit them. On the other hand, Atlus's Disgaea: Hour of Darkness also managed to qualify for GH status in its first year (2003), but it has never been given that status. This is probably because Atlus subscribes to the annoying business strategy of producing their more popular games in extremely limited quantities, with store inventories receiving more copies of their games at seemingly random times, but continuing to sell them at prices of $40 to $50, while a GH release would make the game's price a mandatory twenty bucks.