I've seen the SOFIA, its nice, it was one of the 2 SP's that United painted in their 'bowling shoe' livery. Qatar and Oman still fly SP's as presidential jets, and a few still fly in Namibia.
The Global Peace Ambassador SP (former Pan Am) is still in disrepair.
I saw it in BWI about a year and a half ago, get this, its on the tarmac, next to a ATA L-1011, and crossing right in front of them is a passenger DC-8 charter.
I had no camera, and the weather was lousy, it was the perfect shot.
Here's a link to a picture of the coolest 747SP livery. I wasn't sure about the copyright status, so I didn't post the picture here.
http://www.747sp.com/viewphoto.asp?826