First, an older motorhome with very low mileage is not a good thing. It means that it has sat unused for extensive amounts of time over the years. And that, in turn, means that either it was not in good working order (and therefore sat unused) OR it just sat unused (and therefore the parts have deteriorated from disuse). You're better off buying one with more mileage because it means it was used more consistently (and that means it was maintained better).
Second, a motorhome is basically a "toy". People buy it, they use it a bunch and take joy in cleaning and maintaining it. Then, as time goes on, they get another new toy and put their attention on that. The maintenance on the motorhome starts to dwindle down to the bare minimum. Or perhaps they get sick or get a new job and they can't go out in the motorhome like they used to. It sits in the driveway or storage and they don't worry about getting oil changes, filters, hoses and belts, etc. But regardless why it isn't being used, they finally realize they're not going to start using it again and they put it up for sale.
It looks in great condition, but all those little parts in the engine have deteriorated from non-use and age. It starts up and it looks good, but once you buy it and start using it, those little parts start breaking down.
The point is, buying an older used RV is not a cheap and easy way to go. You are not putting a lot of money into the purchase BUT you will be putting money into the repair/maintenance. You also may likely not have a dependable rig for several years while you do repairs to correct the damage done from the prior neglect (not usually intentional neglect, but neglect nonetheless). If you're not handy with engines, plumbing, electrical, etc., or you're not willing/able to pay others to do that work for you, then you're better off putting more money into the initial purchase.
As for resale, you're never going to get back what you put into it. If by the time you're done with it, it's in worse shape than when you bought it, you might be better off stripping it and selling the working parts (people with older rigs are always looking for spare working parts). If you put a ton of money in it and keep it in equal or better condition than when you bought it, you will be doing good to get what you paid for it.
I've had my 40 year old class C American Clipper for about 3-1/2 years now. I have put triple what I paid for it into repairs/maintenance. Some issues took a lot of research and trial & error to correct, some just took a lot of money. It is now getting to the point where it is reasonably dependable, but I know every time I take it out, there will be something that needs repairing.
I will say that I am still WELL under what a 2-5 year old rig would have cost me. But, I'll never get back what I put into it.
1975 American Clipper RV with Dodge 360 (photo in profile)
1998 American Clipper Fold n Roll Folding Trailer
Both born in Morgan Hill, CA to Irv Perch (Daddy of the Aristocrat trailers)