I agree with
@icarusethan wishing wells on main would be a waste of space once you get to a certain level. When you don't need the goods, don't need the coin, supply, can use that space to create more FP the 1% chance of 50 diamonds don't really cut it as a reason to keep them. Make a diamond farm, diamonds are the only thing that carry over. You have every other world to have as many WWs as you want, funneling those diamonds to your main. Don't waste main space you need for something you can put on another world. My opinions of course.