IMO No I don't think it's worth it. Explorer really needs to get to the port of Orlando earlier. Docking in the afternoon then having to get to Universal or Disney is alittle much.
When are you cruising? Spring break is coming up and the parks are jam packed. Also summers are very busy at the parks. You stated the parks close at 9pm which I believe you are going during a busier time. Slow times they close at 6pm Universal and 7pm Islands.
Both parks Universal and Islands are awesome but getting there at 3 would be very rushed to get to everything.
Even during slower times some rides do have waits. Just checked the wait times for today and Harry Potter is 40 minutes, Minion Mayham is 45 minutes, Hollywood Rip ride is 40 minutes, The Simpsons is 35 minutes and Spiderman is 25 minutes. The first monday in February is considered a slow day.
If you really have your heart set on going to the parks the other option would be buying a fast pass and that will get you in and out of rides in no time. However the pass is additional.
As for the ship setting up a buffet late for the cruisers that miss earlier dinner due to being out I have not heard of this being done....
Have a great cruise!!