If the vehicle or tires exhibit no signs of alignment problems, then there is no reason to have them aligned, unless you
know you've hit something out of the ordinary, like a really deep pothole that rattles everything in the van - your brains included, or slammed into a 4x4 laying out on the road, something like that. If there is uneven wear, have the alignment checked. If it pulls or drifts to the side when it shouldn't, have it aligned. If it pulls when you break, it could either be alignment or breaks (or tires out of balance). Have them checked. No need to have a set schedule for alignment. Also, even in Detroit, rough roads aren't as likely to throw the alignment, as long as the roads are relatively evenly rough and your suspension is working properly. It's the abnormal
wham! that does it.
I had mine aligned a while back, then two days later I hit a pothole that I'm surprised I was able to drive out of. Had it aligned again the next day, and it needed it, bad, even though I couldn't feel any difference in the handling.
I have nitrogen in my tires, so I can't have them rotated just any ol' place (different pressures in front-55 and back-80). I rotate them every 20,000 miles, and each time I have them carefully inspected for uneven wear. So far, so good. If I didn't have nitrogen in there, I'd probably have them rotated every 8000-10,000 miles.
I've got 87,000 miles on these tires, and based on current treadwear I should be able to get 120,000 or so on these before any of them get to the 4/32 mark (the magic number for steers).
This weekend I'm installing the heavy duty anti sway bar and the Koni shocks and struts. I'll keep you informed.