Dollars aren't worth much compared to what they were twenty years ago. I'm expecting that they will continue to decline in value at about the same rate as our Boxsters for the next five years or so, then the depreciation of the Boxsters will probably be slower that the Dollar. Over that five years, I will have spent the $5k to $7.5K that the car is worth on maintenance costs. Like 'investing' money on a vacation, the return is in enjoyment.
They have reached a value where the 'low hanging fruit' is being picked up by people who will not maintain them. Those will quickly turn into the sub-$1k 944s I see on Craigslist just needing 'a little TLC'. This will probably drag down the value on the higher mile cars.