I think it might be bad to directly trade Mogas, but if there's one thing I definitely want to do, it's trade collection cards. I've got way too many of so many of them, I'd love to trade some of them away.
It also has less chance of giving a low-level player too many high-level Mogas (imagine trading someone who hasn't reached Spiral Cave a level 25!); after all, the max level Moga you can get from a collection card is 10, from what I've seen.