I'm unconvinced that a compelling use case exists for the SR-72.
With the real possibility of global tracking of anything bigger than a falcon, me either. This is why, IMO, we just "lost" a satellite. Then again with so damn many birds up there who knows what birds are spy satellites (all of them), what can image your troops in the field (all of them) and what birds can track your electronic signals (all of them). Launch a weather satellite with a special not advertised payload of say a 1M camera, or an elint package. Add on customers to the satellite bus, and if you are already a government agency it may already be happening with the LandSat family for all we know. The Air Force already has a fleet of weather satellites, why not add some extra gear if the power budget allows since the main cost is launch and ops, not building the sat itself. Then you start to get into Alex Jones, tin-foil hate territory of what is possible, what is probable and how you can fuck with people.
I'm wondering if we are going to hit a point in the very near future where there are so many spy sats from so many players that the very concept of war itself is going to go through a radical transformation. Why fight and risk breaking the stuff you want and having to rebuild when you can write checks with lots and lots of zeros, and then hack what you cannot buy?