I am in the same position as the OP but looking for a different rig.If your financing you should also weigh the difference between used vehicle interest rates compared to new vehicle interest rates.
In regards to finance if you buy a current year vehicle with less than x miles you can still qualify for new car rates. I forget the mileage cutoff but talk with your local bank.
Patience is key to a search like this, also you must be ready to move when the right rig comes along. I would expand your search to the eastern half of the country, it's not much to fly out and drive home.
I forget your other question but there are a million reasons why people sell low mileage vehicles. **** happens, low mileage mint cars are pretty common. My last buy was a '12 Mustang I bought in '12 with 4k miles on it.
I am looking for a van with less than 10k on it, '15 or '16. The mileage does not make a huge difference in regards to value but I would like one that has not been driven too much.
I use Autotrader as my main search tool - you will find plenty of vans that suit your needs there.