Is there any point at all in collecting the 3 Easter Eggs and returning them to their stand?

If there is, can I make some ash because no one is selling it and it never occurred to me keep the stuff I found.

If you turn in the Easter Eggs then you advance to the next experience level. I don't think you can make ash, though the shopkeepers get new stock each week I think, or else you can reset a shop inventory by deleting the relevant map file (when your character is not standing in that map).