No, I'd argue that the U-2 platform is the single greatest specialized airframe. It was built ten years before the SR and is still flying today. Not only is it still flying, it is going through another upgrade program to keep it flying, and the Air Force claims the airframes are good through 2050. It is a fantastic machine and is still used for high-altitude observation daily. Sure, it doesn't go as fast but that isn't the point of the high-altitude observation role; the SR-71/A-12 only went as fast as it did to maintain sustained flight at very high altitude and for SAM evasion. With electronic jamming equipment onboard the U-2 you are just as safe from the SAM threat. With the improvement of electronic warfare technology and 'portable' imaging arrays the U-2 will only get better as time goes on.
Pic related: NASA's version of the U-2, the ER-2