Our Spring Break is mid-March. That's the thing about Spring Breaks - they are staggered. No way would I go Easter week, but the other weeks probably won't be any worse crowd-wise than summer. It is Peak season though, so the hotels are expensive.
We went the first week of August this year. Yes, it was HOT! But it was fun, we survived, and I would do it again if that was the only time we could go. It wasn't that crowded. The Unoffical Guide was predicting crowd levels of "9", but it was really about 7 or 8. We never waited more than about 20 minutes for anything, and we did Fast Pass if the waits were bad.