We did a wishing well and I don't think it is rude as it was anonymous. We don't know who gave what or even if everybody gave something. Some people still brought gifts instead which was fine. We lived together before and had quite a bit of stuff and not much space so we put the money to a land deposit. I think you can ask nicely and you can ask rudely but most people feel that they would rather give you something you want or can use, not something you already have.