I own an ambulance company, so I have a bit of experience with E-Series vans (e350, e450's). All of them are powerstrokes, but not that it matters. I have also owned a '95 E-150 custom van and a '02 16 passenger van. Every one of them have front end problems. The ambulances are worse than the plain passenger van or the e-150. They all get lots of hard miles, but also get regular maintenance. I have worked for other ambulance companies for 10 years, and my mom has worked for other ambulance companies for 22 years. I have a lot of experience with Fords in general because almost every ambulance made is a Ford. As long as I can remember, they have all had problems with their front ends.
I think that that problem with ambulances is that they are so darned heavy. A vehicle is normally loaded to a certain percentage of their maximum Gross Vehicle Weight Rating. The closer you operate to that GVWR, the quicker things wear out. A normal unloaded van may be at 50% of their GVWR, but an ambulance is operating at about 85% all the time. That's not including the equipment, patient and crew (who are invariably over 350# each). After all the necessary items are onboard, it really only leaves about 600-800 lbs of extra capacity for the patient before you are overweight.
Anyway, the short answer is that yes, E-Series vans will need constant alignments.
Eli Benson