I'll second, er... third .. nope already taken, fourth nope, fifth no thats taken too. Well then I'll just join the chorus and say arrive in Orlando the day before.
Here's My reasons.
1) you're only going to be on the Wonder for 4 days

which is ONLY 3 nights!!! Remember your first day (Thursday doesn't start until you board the ship and your Sunday on the ship is over by 9am).
2) Is it worth the possibility of missing the ship?? How far away are you comming from? Is the weather the time of year you're traveling good where you are departing from, making connections through and the one you don't know - where is the plane you're catching at home comming from???

Then there's the ubiquitous "Mechanical Failure" of any aircraft at any time.
3) Does the three or four hours on embarkation day make a difference?
YES!!! Here's my story. Our first cruise was in '99 when only the Magic was in service. We were at WDW. Our cruise documents said that boarding started at 1pm. I figured that since they didn't start boarding until "after lunch time" that we would need to eat before heading to the port. So we stayed at the resort and had a peaceful morning, swimming and packing and getting ready for the cruise. Then we had lunch. Then we started out for the port around 12:30 (it only takes an hour or so to get there). Well once we were there (after 2pm), there were thousands of people, long lines to get checked in and a long line to board the ship. We finally got on board found out that there was a lunch buffet so we went there and had second lunch ("free food"

). Afterwards went to the stateroom and started to unpack. Went out and explored the ship for a very short time, manditory safety drill, back to the room - our bags were there so did a few minutes of unpacking (clothes for dinner) up to the sail away party, back to the room to get cleaned up for dinner, dinner (wasn't really hungry), show afterward, dancing and partying then back to the room after midnight. Whew. Ok were's our stuff - oh yea, it hasn't been unpacked yet!! Well unpack what we need, toiletry's, pj's then off to bed. Up early next morning for breakfast and excursion - hey where's the swimsuits - oh yea, still in the luggage that we're climbing over. Sometime late that afternoon we were finally unpacked and our room "organized" for the next two days. If we arrived earlier and were closer to the "first in line" we would have had a much more relaxing first and second day on the cruise.
4) The terminal is NOT a boring place to wait. It's a beautiful building. There's the model of the ship inside and the real one outside. There are soft couches and TV's playing Mickey Mouse Cartoons. The characters make an appearance. And like at the parks, it's better to be waiting in line "outside" rather than waiting in line "inside". If you want Palo or spa ressies, there's lines to be waited in inside. The earlier onboard, the less of a queue to be waiting in.
5) The few extra hours onboard by being at the port early will allow you to make ressies (if wanted), enjoy lunch, do a little ship exploring, get to your stateroom and maybe start unpacking (if your checked luggage is there), swim in the uncrowded and clean pools before the manditory safety drill and give you a chance to unwind and enjoy your vacation.