As the topic says this event gives very good rewards but getting those pies or gelt on a character that don't use one of them is a waste, especially since you cant get them in any other way and they are the best attack pot. Now for me gelts are so rare i really don't wanna use them and Apq has a low apple rate. Right now i have 18 graham pies and i think they should have some purpose, and as a Thief they have no purpose. The bad side of this, it would make Onyx apples and APQ less beneficial i see already that apples become less expensive and sought after. But that will most likely change attack pots are not lasting.
If they were to implement this for the remainder of the event, they would have to lower the rates at which these items are received. As it is, getting the wrong atk pot functions as a "waste" item to keep the rare things rare. Making them switch-able doubles the rate at which you're able to get the attack pot, which would lead to an "overdose" of them in the economy. I don't think it's worth changing.
The entire point of them is to be hard to get and somewhat rare. By having either potion available, the chances of getting the one you need become just a little more slim and make them just that much more rare as well. By being able to exchange the one you want, there wouldn't be any rarity to them at all.
I would not classify Banana Graham Pies as rare by any means. I don't think we should necessarily be able to exchange them, but I do think the rates at which they are given out is a bit of a design flaw. I have a total of 24 Banana Graham Pies across 2 characters, and 0 Gelt Chocolate, and I know many others with similar stories. I understand that Banana Graham Pies were intended to be a little more common, but it seems extremely imbalanced to me.
I'm the exact opposite. I've had 3 banana graham pies and a total of 18 gelt chocolate on my BM, and no banana graham pies and 9 gelt chocolates on my mage. I'd be willing to bet the rates are pretty similar, and you've just been unlucky while I've been extra lucky.
The rates for each of these items are the same, I would think it to be a bad idea to implement an exchange mechanism this late into the event. As already seen, some people have thrown their useless potions away. And of course, not every single reward you get from the snowman is going to be fantastic, otherwise it would be too overpowered.