The only possible issue with saving the ticket to upgrade later would be if Disney changes their tickets to something different from the current MYW tickets. In that case, I assume the MYW tickets would only be able to be used as-is, similar to how the pre-MYW park-hopper tickets cannot be upgraded and just used as-is. Because of this, when we needed to purchase tickets with a package this summer when we'll have AP's, I purchased tickets that we'll be able to use as they are without upgrading. We purchased 10-day non-expiring with the water park option that we'll use on future trips when we don't have AP's. I'd rather purchase that than a one-day ticket that I'm afraid would only be good as a very expensive one-day ticket that cannot be upgraded. But, I'm probably just pessimistic that as soon as I purchased a ticket with the intention of upgrading, that's when Disney would change their ticket structure again!