IMHO, once all the baby Boomers die off, there will be a huge surplus of "Classic" Porsches that the Boomer generation grew to love an covet.
Surplus+lack of appeal = Worthless
The following generations seem to care less for the "Race" heritage cars and like the SUV types better.
So as any investment goes theres boom and bust.
The Boom is currently here with the retiring Boomers picking up the cars they love to enjoy before its too late for them. They have the money so cost is no problem.
In 30 years all the Boomers will be dead and along with it the value of those classic cars, which will also be 60 years old by then.
Enjoy what you've got now and don't worry about the value of "Classics"
If you love it, is all that matters, no matter how gorgeous or ugly it may be.
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"It broke because it wants to be Upgraded

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2012 Porsche Performance Driving School - SanDiego region
2001 Boxster S, Top Speed muffler, (Fred's) Mini Morimotto Projectors, Tarret UDP,
Short Shifter, Touch Screen Dual Din Radio, 03 4 Bow glass Top (DD & Auto-X since May 17,2012)