The people who are spending $200 on a cartridge are doing so to have that cartridge, it has nothing to do with availability of the game itself. Unless you start printing up new copies of the original SNES Earthbound and flood the market with them, there is no way this will affect the value. Joe Gamer who wants to play Earthbound because he's heard so much about it is not the person paying $200 for the cartridge. MasterBelch2782 who is obsessed with the game and wants to own the original cart isn't going to care that he can just download it on the Wii U, it's not the same as owning the physical cartridge, he will pay $200 to own it.
Your theory is flawed because you are assuming that the price is being driven by the game itself, which it is not. The price is driven by the intrinsic value and perceived status one receives from owning the actual cart.