Actually, the ACS712 is not a good match to your application. It is a linear sensor which means you get a voltage output proportional to the measured current. This comes at a cost - both the IC chip (relative to a cost of a bridge-rectifier) and, to your point, additional circuitry to convert the output to a yes/no digital signal as needed by the downstream circuitry. It appears the 1.4V "tax" and arguably punitive power dissipation are acceptable so really all I can say is thanks for sharing! 
One observation about the thread topic of "current detectors". From what I've seen the big effort in block current detectors is for 2-rail applications like HO where they don't have the luxury of the extra isolated rail for "free" occupancy detection. 2-rail being generally DC, the bridge-rectifier and ACS712 operate/detect DC currents as well as 60 Hz AC and high-frequency DCC. I suspect if 2-rail had historically been 60 Hz AC, there would be more published circuits taking advantage of doughnut current-transformers as occupancy detectors without the 1.4V "tax". Not quite apples-apples but we all have current detector circuits protecting our safety - the GFCI (Ground Fault Circuit Interrupter). Generally implemented with a low-cost application-specific IC chip, it is a clever circuit which can detect remarkably small AC currents generating what amounts to a yes/no output.
