I added airbags thinking I would need them and also found they made the ride worse. I now keep them at the minimum pressure the manufacturer recommends, which is something like 10 psi, but I can still feel them. The back definitely feels more bouncy with them on, and it bounces at a faster frequency which is less comfortable than the sort of wallowy bouncing I got before. I can see that if your front shock absorbers were tired then the rear bouncing more might mean that instead of the rear suspension absorbing the movement, it could be acting more like a pivot so the up and down movement is translated into a rocking movement.
Steve.