March is prime spring break for many places, no matter when Easter falls. If you want lower crowds, only the first week of March would qualify - and it's usually a great week of moderate crowds and nice weather. But, spring break will hit with a vengeance the second week of March, which is rated a 9 by Touring Plans.
Josh has posted recently about how they're not fully staffing the parks during slower times anymore, so you might wait just as long during low crowd periods as you would during high crowd times. He didn't mention MM+ as being a factor, but I think you're 100% correct on that.