I was told they lost both ERAM and EBUS (the new DARC system)... so they had primary radar but no secondary radar. TRACONs/Towers were unaffected as far as I know.
Regarding "squawk tactical": Most of these things are classified information, but my best educated guess is that it's a specific beacon code assigned by Letter of Agreement between the facility and the military unit.
If we say your call sign, you have established communications, thereby meeting the requirement. If we say "aircraft calling, standby", you cannot enter. The book is correct.
I'm obviously not going to be an official commentator on the cost (since I don't know dev costs), but if we hypothetically expanded to all ARTCCs, you would need to pay a very large sum of money simply for FAA data that we use. It doesn't come cheap. Then factor in controllers to staff the facility ...