I know what you mean, I hate getting rid of stuff if it's going to be reaaally hard/annoying to get back no matter what I get in return. 
Actually, I think the PuPu card is the only missable card in the game, isn't it? Apart from that the others can be gotten again from elsewhere. I think.

Actually, I think the PuPu card is the only missable card in the game, isn't it? Apart from that the others can be gotten again from elsewhere. I think.