[quote name='Frosty The Batman']So should anyone that has MvC2 on PS2 sell it now and re-buy after the price declines?[/QUOTE]
The situation is not exactly that cut and dry. I typed up a whole example, but I couldn't make it simplistic enough to even type in this forum.
I decided on this simple example and explanation without many details:
As of now, Castlevania: SOTN is available in three (or more???) formats: PS1, XBLA (digital) and PSP. Collectors are still willing to pay a heavy premium to get SOTN for PS1, black label and still brand new and sealed in the original wrap.
Obviously, that scenario does not always happen.
One big factor to consider is the title's format. The PS2 version of MvC2 may actually be scarce. Thus, regardless of its reproduction in other formats, collectors with resources will still seek out the title.
By looking at Psychic Detective for PS1 and 3DO, we can find a simple and suitable example. The game is a pile of shit, and the 3DO version is superior. Because the PS1 version is more difficult to acquire (at least according to DP and various other sources), a used PS1 copy is about three to four times more expensive than its 3DO counterpart. On eBay, I've seen sealed ones sell from $50 to $100. Unlike MvC2, that game is not even popular.
There are so many factors. I feel foolish to leave any out. Unfortunately, we would need to create a good model to take into account most of them.
In the case of MvC2, here is another factor: a new copy will not as easily fall in value, compared to, a used copy. So, a used MvC2 could possibly end up losing value, but the new ones could fall by a smaller amount, stay stable or continue rising up in value.
Obviously, if a title is available by digital download, then we would have to consider that in our assessment. IMO, the Castlevania: SOTN example is a much closer representation of the possible upcoming situation.