They do when they’re flying the opposite direction as you.

Also, he’ll if we civilians know what kinds of retrofits have been made in the past several decades, particularly for the purpose of testing and development.

The U2 is a very well-understood and photographed airframe. Even if given engine upgrades, it wouldn't be more than a few mph faster than before. Those big glider wings limit it to a very narrow, predictable, flight envelope.