t4halo,
That is an "it depends" question.
The earliest models had pressed wood cabinets and cab over bed floor. If well cared for that is not necessarily a problem, however, I have seen many older FWC campers with degraded over cab flooring due to water damage as well as chips and dings in the cabinets that exposed the pressed wood. Also the wood grain on the pressed wood was actually paper with a wood grain print on it. Repairing any damage to those cabinets is not worth the time or trouble in my opinion.
I am not sure when FWC went away from using pressed wood.
The earlier campers used a different material for the flexible siding that had an insulation material built into it. I have seen two major issues with that material. 1) It became brittle over time and started cracking and 2) a lot of these seemed to develop black mold from condensation.
I am not sure when FWC switched over to the material that is now used on the campers.
As I have written elsewhere, I have a friend with a 1983 or 18984 Keystone (he is the original owner) and it has always been stored inside with the top up. The pop-up side material (so called canvas) is still flexible with no holes and there is no mold damage, While the interior fabric and cabinet finish is dated it is still in very good condition. They will be accompanying us and driving their 1993 Doge Diesel with this camper to and from Anchorage between late August and early October this year.
I had a 1984 Keystone that I bought used and it was in much worse condition than my friend's camper. The end panels were deteriorated, the cabinets were beat up, the over cab floor sagged and the canvas had staining (and shortly after a little use developed pinholes). I bought it cheap and had planned to refurbish it before I came across the 2007 Keystone we have now that I was able to buy at a very good price and which was not much more than the aggregate cost of refurbishing the old Keystone. The old Keystone did have good bones but I figured it would cost me at least $5,000 or $6,000 to refurbish it even doing the work myself (but buying pre-made end panels and pop-up siding).
The main thing I miss about the older Keystone is the size. the floor was wider and the interior felt roomier. Wendie misses that too.
The things we like about our newer Keystone. The larger over cab bed (ours is Queen size). The slide out bed extension vs the fold up bed extension with Aluminim legs in the old Keystone. The rollover couch in the new Keystone vs the old couch design with aluminum legs in the old Keystone . The pop-up siding material seems more robust in the new Keystone.
The cabinets seem to be a bit better built in the new Keystone however they are not solid wood and the "wood finish" is actually a wood grain printed paper which will permanently degrade if it gets wet and it gets rubbed just like the old Keystone cabinets. The IOTA charge controller is better than the charge controller in the old camper (I forget the make).
The sink, stove, water tank and propane tank were comparable between the two campers.
So if you are handy, have the time and enough cash to buy materials and you want a nice camper customized to your needs but don't want to spend over 10 or 12 K it may make sense to refurbish an older FWC.
My guess is that if you buy ready made, new side material, and end panels the cost is going to be upwards of $3000 from ATC (not sure as I have not checked recently). There are folks posting here that have made their own siding and end panels as well as installed them for less than that. Similarly for cabinets and headliners.
The hardest issue to remedy, unless you can weld Aluminum, is making the over cab bed larger than double (if that matters). You would have to strip the camper down to the bare frame to make an over cab bed size modification.
If you find a well cared for older camper I see no reason why it would not be worth evaluating.
I would ask lots of questions and look at lots of photos first. Here is a link to a reasonable used camper buyers checklist:
http://www.wanderthewest.com/forum/topic/3449-four-wheel-campers-used-buyers-guide/
FWIW: We traveled from Solvang, CA to Montana to buy our 2007 Keystone after I satisfied myself via lots of email Q&Q message exchanges that it was worth the trip. I do not regret the decision. We like our camper a lot.
I hope this is of some help.
Craig