We too went for Spring Break 2005 and it was crowded but we had a blast. We got to ride/do whatever we wanted to do just by planning ahead. This was rumored to be one of the most crowded Spring Breaks because all of the surrounding counties in Florida had the same week off, plus it seemed tons of other schools coincided too.
Here are my best survival tips:
Early EMH is great! We found it especially helpful at MK, and a complete waste of time at AK. During our trip MK had early EMH every morning we were there. It opened for resort guests at 7am and we got everything we wanted to do there done by 2pm. Around 11am-noon it started to get crowded and pretty much stayed crowded. MK was open to the public until Midnight every night we were there and until 3am on the nights they had late EMH. We were not there for a late EMH but considering the park re-opened 4 hours later, I would think the best day to go to MK would be the morning after late EMH there. As for my opinion of AK, everyone makes a mad dash for the Safari or It's Tough to be a Bug and it makes it kind of pointless to go early just to have to FP the Safari ride anyway (IMHO). We did not go to MGM or Epcot for EMH so I can't comment.
If you want to eat in a restaurant, have an ADR. I wouldn't recommend too many ADR's though you want to keep your plans flexible in case you have to park hop to somewhere less crowded.
Take advantage of park hopping. I don't think I'd consider it optional when the parks are crowded. If it's bad in one place, hop elsewhere.
Fast passes can be your best friend. Use them if you need them.
If it's warm enough for a waterpark day and you want to go, go first thing or you may not get to go at all (capacity).
If you want a good seat for a parade/fireworks/show, find a place 45-60 mins before the start time. Get a snack and eat it, find a curb or something to sit on and take that time as a time to rest your feet.
Bring a jacket, sometimes it was kind of cool out, especially at night.
Bring a good, positive attitude. That will get you through more trying times and frustrations than a park hopper or awesome ADR. Planning is good, over planning can be stressful. Pace yourself, schedule time to look for hidden Mickey's in bushes and always remember that you are all so lucky to be at the Happiest Place on Earth, whether it's crowded, hot, or rainy.
Have fun!