The drive to catch all 493 beasts in Pokémon Diamond and Pearl is causing a surge in demand for old Pokémon games. JJGames' used video games price tracker shows the average price for used, classic Pokémon games rising over 20 percent since early Feburary. Used game prices in general went down nearly 20 percent during the same period.
As the above graph shows, the Pokémon prices largely track with the market through the end of February, when they surged ahead of the DS games' April 22 release. The prices take a downward turn for the month after Diamond and Pearl's release, then shoot up again after Memorial Day, the traditional start of summer.
While this meteoric rise might encourage you to invest all your savings into used Pokémon games, we encourage caution. A well-diversified portfolio of used games is the only way to avoid fiascos like this one.