I am curious to hear what the MMM community has to say about this, because I have also looked into it.
A few of my thoughts, in no particular order:
Yes, mobiles/manufactureds lose value. You are, however, extracting value from it while living there, because a) you have a place to live and b) presumably you're paying less / month for lot rent than just renting a place. Or, like you said, if you have an MH on its own lot, even better. I worked up a basic Excel sheet to calculate the net financial effect of buying an MH....including lot rent & maintenance vs. apt. rent, assumed buy/sell prices, etc. With a few assumptions you can easily calculate a break-even date. For the numbers I've run so far for my situation, after 1-3 years I would be ahead having bought a mobile.
There are, of course, a lot of things to watch out for when looking at an MH. In the olden days they used to use aluminum wiring, and that can be a safety hazard. In a lot of jurisdictions, you aren't allowed to set a mobile that doesn't meet certain criteria, which usually works out to mean anything older than (I think) 1976 has to stay where it is (unless there's a nearby county with laxer codes :) ). Etc. etc. etc.
That first link has a lot rent of $876 a month! Like you said, that's not much better than where you are now at 1100ish. In my area, lot rent is more around 1/2 of a decent 1-bedroom apartment.
I just don't see taking out a mortgage for a mobile, myself....at least not for one of the lower (OK, not bottom-o-barrell) / mid range that you're looking at with 25-40K. Personally, if I had the cash, and I were paying what you're paying for rent, I would find myself something different. But you're in a different market.