If it can be shot down, I think that it's probably safe to assume that it won't be able to see anything particularly interesting. I'd expect something like Groom Lake to be surrounded by an impenetrable wall of interceptors and SAM sites.
Though I suppose that you could try to make your drones so cheap and in such volume that shooting them down becomes logistically and economically infeasible, but that's another strategy entirely.
> I'd expect something like Groom Lake to be surrounded by an impenetrable wall of interceptors and SAM sites
The whole idea of the SR-71 was that it went so fast that SAMs could just barely not catch up to it before they ran out of fuel. Any other plane couldn't outrun them, but the Blackbird? Well, Mach 3.4 will give you some breathing room.
More to the point, it takes time to notice, track, lock and (in some cases) get approval to fire. That gives you seconds to minutes to not only fire but for the missile to reach the intercept point.
Missiles and radar tend to operate in a "bubble". Even with the Russian S200 system at 190 miles range, the time you spend in that "bubble" when you're at 70k ft is not often long enough to do anything. That also assumes the aircraft directly overflies the battery. You can play games like pointing the camera sideways and observing from an angle if you know there are going to be angry people with guns nearby.
Mach 3.4 was also fast enough that early radar systems couldn't track it. The plane would move far enough between radar pulses that it got filtered out as noise.
The state of the art advances. There are SAMs today that can shoot down ICBMs. I would guess that one reason the SR-71 was retired, besides the official line that it was expensive and made obsolete by satellites, is that it was no longer invulnerable as it had been when it was new.
Though I suppose that you could try to make your drones so cheap and in such volume that shooting them down becomes logistically and economically infeasible, but that's another strategy entirely.