We often come home with extra days on our ticket but it isn't worth it to add the no-expiration on. We usually go for 12 or 13 nights and get 10 day tickets which gives us the flexibility to go into the parks for 10 days, even though we have some trips that we only go 8 or 9. The difference in price is so minimal that it is nice to know that we can go into the park on one of our "off" days if we need/want to. Since we go in August, we have also run into hurricanes/tropical storms where we are forced to leave the park early on one day so then we can still go back on another day since we have the longer ticket.

It does stink "losing" a day on a ticket but since there is a possibility that we will use it, for us it is worth it.

If you are REALLY sure that you won't use the 4th day, it may be worth it to save the few dollars and downgrade to a 3 day ticket - even if it is only a couple of dollars. Or, my favorite option is to add another night to your trip!