gold
There is some gold out there. Australia was flooded with new GA aircraft two or three decades ago, and most of these aircraft are still here. Some are in good shape and some are not. Those that have been properly looked after are still very good. Engineers can assess their condition, but too many have learned to accept low standards, and cost pressures over the years have produced some rattly machines. When a LAME signs an MR, that means he considers the aircraft will be safe to fly for another year, or another 100 hours. It does not mean it is perfect.
However, there are many aircraft out there that have only flown two or three thousand hours, maybe five. There are quite a few aircraft out there that have flown over 20,000 hours, and still going. I read recently that the first C172 that was ever built is still flying in the US. When I went to visit the Pacific aviation factory in NZ they told me that the first Fletcher AG plane they ever built (in the sixties) was still flying, doing survey flying, with about 25,000 hours. I think it has a turbine engine now.
Most GA aircraft in Australia have realistic life of about 10,000 hours, with routine maintenance if looked after properly, and about double that if you do some structural work when it is needed. Some can go much further.
If you are one of those who have to have the flashest car in the carpark, and would not be seen dead in last years model, then maybe these are not for you. But a 30 year old metal aircraft in good condition that's flown 20% of it's useful life, is about as old as our military aircraft, and flown a fraction of the hours that the Qantas aircraft have, is pretty good value. If you get a good one.