If it helps, we only had an alignment check 1 of the 38 Mirage's we have here at work here. We got it checked (at our cost) by an independent shop cause the rear wheels looked off, turned out to be fine and the tires all wear fine if they are rotated regularly. Had the rear axle been bent we would have taken it to the dealer and request they fix it and reimburse us for the cost of the alignment.
I can see how many dealers don't want the hassle since most Mitsubishi dealers (at least around here) are small and have to farm out alignments so they'd have to pay someone to drive the car there and back as well as cover the cost of the alignment on a car that probably doesn't have a problem in the first place.
If it's a good deal and it's the car you want I say go for it as long as you're happy.
And congrats on being a dad soon!