The prices of rares will rise in terms of GP, no doubt. The question, though, is how far GP prices will plummet. Eventually, I see them going to $0.05-$0.10 or below - $0.01 per mil, for example. In this case, the price of rares, in real cash, would only increase if the GP value soared above 500b, which, I think, is unrealistic.
Therefore, I would sell rares if I had any.