There is an interesting article in the April 2015 issue of Grassroots Motorsports about the rising values of older enthusiast cars. They source the values from Hagerty Insurance and compare the values of specific cars in 2012 to 2014. The 1992 Mercedes Benz 500E is one that seems to have appreciated extremely well. I listed a few of the other notables as well. In a separate article they listed the Mercedes 190E 2.3-16 as a great buy that has the potential to appreciate.
Car 2012 Value 2014 Value
'92 Mercedes 500E $7,800 $36,700 (http://www.hagerty.com/valuationtools/HVT/VehicleSearch/Report?vbe=119008)
'88 BMW M3 $17,300 $44,000
'77 Porsche 911 Turbo $44,300 $130,000
'91 Acura NSX $29,700 $39,800
'88 BMW M5 $12,600 $20,200
'93 BMW M5 $13,500 $21,800
Car 2012 Value 2014 Value
'92 Mercedes 500E $7,800 $36,700 (http://www.hagerty.com/valuationtools/HVT/VehicleSearch/Report?vbe=119008)
'88 BMW M3 $17,300 $44,000
'77 Porsche 911 Turbo $44,300 $130,000
'91 Acura NSX $29,700 $39,800
'88 BMW M5 $12,600 $20,200
'93 BMW M5 $13,500 $21,800