The SR-71's high speed and altitude was useful, and worth its high cost, for two reasons:
1. It was impossible to shoot down.
2. You could go check something out on short notice.
#1 doesn't really matter with drones, especially if you're not going to overfly the target country. #2 is easily solved by keeping a bunch of slow drones in the air all over the place at all times, rather than keeping fast aircraft ready to fly.
Interestingly they were already experimenting with drones back when they were flying the Blackbird - I wonder how good they are now?
These are to augment current capabilities, especially if there's escalation of hostilities. If there's a conflict in the Pacific, we cant rely on having our forward air bases. Most likely these will be launched from domestic locations and ingress/egress time will have a large impact on total coverage time.
From the fine article: at Mach 3, the target can still be notified, at Mach 6 it's unavoidable.
Don't know if that's true, but it does answer the question.
So moving things out of the way {of the lens|of the bomb} doesn't look like that much of a difference .