A 3rd yr workcamper of ours ( single handiman) has a '78 29' Sportscoach MH. It is immaculate and still has--- all original appliances.---- except water pump. Its a hoot to step into an rv and see there is no microwave, an 8 track, push button radio tuner. Goofy looking thing. Winters he travels south to volunteer. Some camps wont have him because of their 10 yr old rule, but he does better by going to places needing workers then setting up on the jobsite! A class act.
Then there is the annual return guest with matching '67 Chrysler Newport and ''67 Airstream. He did replace the fridge when they couldnt keep the pilot lit. Everything else is original. 50 YEARS.
Lesson is, its not how old, it may be the build quality of those older campers and the use.
If I were you I'd buy old and cheap then keep $ in your pocket to deal with the possible breakdowns. Dont buy an extended warranty. You are right in your quality choices, Tiffin, Newmar. The rest is jobber parts , THAT HAVE NO, reflection on the builder.