I think we are all saying about the same thing, the question is really how many frogs do you have to kiss before finding the right one, when shopping for any older coach. As to the plastic aging, this is another reason to buy what was sold as a higher end coach, as they tend to have less plastic interior items, ie a fiberglass shower in an upper end coach be be showing a few stress cracks in 20 year old motorhome, but a plastic shower will be brittle and crumbling. The same goes for kitchen and bathroom sinks, molded corian or stainless steel sinks may show some signs of age, but will likely be functional vs the low end plastic sinks which have yellowed and brittle. Neither of which helps with the plastic and rubber parts that are mechanical, think steering and suspension bushings, generator fuel line, rubber sections of brake hoses, propane regulator diaphragm, then of course there are the RV appliances many of which seem to have about a 15 year service life (air conditioners, refrigerators, water heater, etc.).
When I started shopping for my current coach in 2016, I had decided I wanted a Safari Trek, production of Treks stopped in 2007, so I knew I would be buying used. The first one I looked at showed up for sale just 3 miles from my house, a week or two after I started considering a Trek, it was a private seller, asking $9,0000 for a 1996 2830, it looks good in the online ad photos for the price, so I went and looked at it. This was a real lesson in what selective photography and low resolution ad photos can hide. While I would not say it needed to be towed to the junk yard, it was close, the seller was down to $4,900 or make offer when I walked way. Just adding up the stuff that was broken came to well over $10,000 (generator, air conditioner, water heater, refrigerator, ...) not counting the water damage, and cosmetic stuff, or that the tires were ancient, perhaps original. Eventually after much shopping, I bought my current coach from a private seller 1,100 miles away for a bit over $20,000, it was the same floor plan as the money pit one I had looked at close to home, but 6 years newer, and in MUCH, MUCH better shape. This is not to say mine is perfect, there are some paint blisters I need to have fixed (local body shop has quoted about $2,000 to fix the worst of them), even though the previous owner had replaced the living room carpet, it is getting time to do it again, ...
p.s. regarding the last post, people that could afford a Unihome Foretravel when it was new, could also afford to keep it in a climate controlled garage. It is simple economics, it makes far more sense to keep a million dollar coach in a $200,000 garage than it is does to keep a $100,000 coach in a $200,000 garage. Of course a 20 year old Foretravel U320 in good condition is still going to sell for around $75,000 today.