I've been contemplating this also.
My ds is 4 and will be turning 5 just before the trip.... He does not really use a stroller any more, but we did take our umbrella stroller to WDW and even though he walked most of the time, it was nice to have when we needed it....
I actually think we will use it zero on the cruise.... But I'm mainly thinking about the airport- we have a long 8 hour flight and we leave crazy early in the morning going there and arrive crazy late at night on our return flight. Plus we have layover's each way. I'm worried he will fall asleep and be too cranky/tired to wake up and walk- having to carry him across the airport would be horrible! So, for that reason I am seriously considering taking our umbrella stroller....