My girls will be 5 and 8 for our cruise in November. I was planning on spending 2-3 days in the parks before the cruise, but the more I looked at it the more I realized we will be so rushed, and it's incredibly expensive to go for just a few days - it would cost our family of 4 just about $1000! They had a blast on the Wonder this past December, so I know they will be happy knowing they are going again. That being said, we are DVC members so we're staying on property a few nights before the cruise, we'll have 2 full days. I plan to spend time in the resort pool, Downtown Disney, and monorail hopping. They also enjoyed renting the 4 person bike at the Boardwalk, so that's another thought.
As for transportation to the port, I've been doing some research on this. Like others have said, it's ridiculously $$$ to use the Disney transportation - $320 for us! We plan to rent a car the day before our cruise and drive down to a hotel near the port that provides shuttle service. There are a lot of options and I've been watching the Trip Advisor reviews. We have a 7:25pm flight home, so we'll rent a car after we disembark. My original thoughts were to spend some time at the Kennedy Space Center or Downtown Disney, but some other posters have mentioned renting a day room at the MCO Hyatt for $100. That might be a great option, since we'll be with my in laws (they are just coming on the cruise, not spending time in Orlando a few nights before with us) and they might be exhausted. In any case, renting a car seems far more reasonable than any type of bus or car service.