It is no doubt that, in most cases, the older the coach the more money you will spend replacing stuff. However, if you shop carefully for a used coach of high initial quality that has been properly maintained, it can be a good experience.
Our first used DP was of decent but not high quality, was 3 years old when we got it, had been well maintained. We used it a lot for 8 years and never had anything break that prevented travel or spoiled a trip. There were things to fix and I fixed most things myself. The most money we spent on anything was usually doing some sort of upgrade that we did voluntarily... new TV's, residential fridge, new Satellite dish, new furniture, new flooring.
Our second, and current DP, is of high quality and was 6 years old when we bought it. It was well maintained by previous owner. We have put 25K miles on it and the only issue that interrupted a trip was a fuel issue with the Cummins diesel engine. 3 days in a shop in TX and we were good to go. Had to fix or replace a few things but we did buy a service plan that has paid for most everything, less our deductible. Again, the most money we've spent was voluntary upgrades.... new carpet, new sofa/chair, new Sat dish, new TV's.
Have we spend more $$ on fixes, repairs on these two used rigs than we would have during the initial years of a new coach... yes. However, we got so much more and better, IMO, coach for what we paid by buying gently used. Plus, we did not eat the huge depreciation with a new coach.
Our only trips to the factories (Winnebago and Country Coach) were voluntary and on our planned route while traveling.
Any of these beasts can be money pits. Traveling in any class A is not cheap but we really enjoy it.