I definitely prefer window vans or conversion vans, life without windows isn’t for me.
I don’t think mileage is as important as maintenance. Most privately owned vans have had decent maintenance, unlike most commercial vehicles that are hacked together to keep them in constant service. I’ve ran the older 70’s and 80’s vans to well over 400k miles, newer ones get really expensive past about 100k miles, and many of them even before that. The more electronics they have, the worse they are, because electronic components tend to fail much quicker than mechanical ones. If I never own another computerized vehicle, it would suit me fine.
Conversions can range from simple, easy, quick, and cheap to very expensive and time consuming. After trying the expensive route, I’ve decided that the cheap route is better for me, not because of the money though, but because I like it better. Everything about my under $300 conversion is superior to my $20k+ conversion. Both comfort and convenience are vastly improved, without sacrificing anything.
With proper maintenance, any fully depreciated vehicle should hold it’s value, or maybe even increase in value. Loan interest and depreciation are the tow biggest killers of any savings, short of traffic accidents or natural disasters. Newer vehicles tend to age much more quickly than the older ones.