The fake Genesis carts listed in the first post look different compared to real copies, Musha is using the wrong casing. If it's easy to tell that the games are fake I wouldn't care that much. It's still cheap garbage but it's easy to avoid. I don't think fakes will destroy the collectability of real copies, people will always want real ones for their collection.

As for GBA games, most are cheap because most games are horrible garbage and it's not old enough to be really nostalgic. Once real nostalgia kicks as it gets older, cheap games will start to spike. As it is there are a bunch of specific titles that are already expensive.