I don't think EarthBound's price is going to change at all if Mother 2 hits the Japanese Virtual Console. That is meaningless to the prices of EarthBound, only the prices of Mother 2, which are already pretty low.
It's 2013 now. If EarthBound was released, I don't think it was have the same kind of impact it would have a few years ago. The hardcore gamers would take notice, but I don't think the Virtual Console gets the attention from casuals as it did a few years ago.
Also, SNES RPG prices seem completely unaffected by digital releases. Prices are still high for Chrono Trigger, Final Fantasy 6, Final Fantasy 4, Lufia, Secret of Mana, Mario RPG, you name it.
I don't see the prices changing by much.