Do not buy a Boxster if you want an "investment".. It will be another 20 years until there returns some "collectibilty" to this model.. so if the first ones were built in 1997, you get to wait till at least 2017.. maybe more. (assuming we are allowed to have cars in the US by then blah blah
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in the future, the "S" will be worth more than a Normal, conditions being equal. Look at 356s today.. or 911s from the ealry 70's.. in either case it took DECADES for them to become collectibles. As a kid in the late '70s and 80s, you couldnt GIVE AWAY a long hood 911. Who wanted such a small displacement motor... and bad HVAC etc etc. That's when enthusiasts bought them and built RS clones and starting having fun.. So much so that the amount of unmolested examples became scarce, people were full of "easy money" and wanted to relive their youth.. so the prices shot up. (I know, simplified)
I think, actually, that the 944 Market is now beginning to turn. Much like the 914 market that turned about 3 years ago, 944s are becoming scarce, especially low mileage, umolested versions. They are the car of "another generation" that is hitting its middle age and wanting to relive its youth. And 944's are 20-25 years old.
If you were 15 and male when the Boxster first arrived, well... when you are 40ish and have some disposable income, it may be a car you might want to finally have to relive your youth..