I think it depends on several factors:
1. Type or Model of unit.
2. Price of unit (I assume anyone considering an older unit is not blessed with the financial means to afford new).
3. How well the unit has been maintained.
4. How willing and able you are to do minor repairs yourself, (or pay to have them done).
Further explaining the above list:
1. I'd stay away from most anything which the manufacturer is no longer in business, especially oddball models which you have never heard of, and never see anywhere. If it is a brand & model you still see rather frequently, that is a good sign.
2. If you get lucky & find decent one for very little money, you are not risking too much, and don't have too far to fall.
3. You don't want to have to change an engine in any MH. Make sure oil is not thick or black, no knocks or rattles, no smoke from tailpipe on startup (unless it's a diesel, of course).
4. If you perform your own car maintenance, and do some household repairs, (paint, replace water heater, etc), you are a good candidate for owning an older RV.
Many of the repairs you might face are minor and easier to do then one might think. And you may not need to do any, or at least not many, if an RV tech took care of your unit.
We have a 1988 Coachmen Classic 31' unit, which we bought at a great price a couple years ago. Had several trailers before it.
Had 32K miles, 454 Chevy (a SUPER engine), had obviously not been driven a whole lot, but needed some minor fixing, still needs a bit more. It has worked out superbly for our needs, and been rock-solid reliable on several long journeys. Based on a GM P-30 chassis, (same as most of the old brown UPS trucks, I believe).
The good news for you, is that most of the appliances, fixtures, powertrains, etc are made by independent companies, not the RV manufacturer, so you can still get parts or replacement units for your A/C, Water Heater, Fridge, Engine/Trans, Generator, Range, etc. And replacing some of this stuff is so inexpensive, quick & easy it's surpising. Water pump? About $30, and 10 minutes, using channel-lock pliers, wire crimping tool, & a screwdriver. Oil change on a gas V-8 unit is about the same as doing a pick-up truck. I think you said it was a Southwind unit, which I see several of in that age range, in our area. I think they are less susceptible to water leaks/rain damage than most of that era, due to shell design. Good looking, too (In my opinion).
I'd go for it, if the engine is in good shape. Probably a 454, which will last forever if you do 2 things: 1. Keep the oil clean, by changing it often & using a good quality oil (Valvoline is unsurpassed in my 41 years of driving & working on vehicles), & filter (AC Delco, Fram or Wix. Use the longer 1 qt filter, not the short one). 2. Do NOT run this engine hard until it warms up. Really, these same principles apply to most any engine. I cringe when folks fire up & jump right out onto a highway. Not good for anything, especially a large engine pulling a heavy load. Best of luck, if you buy it and you do need to diagnose or repair/replace anything, I am sure the fine folks on this forum, as well as fellow RV'ers anywhere, will be glad to help you out. -Dan.