Is this a symptom of worn out torsion bars?

Torsion bars, like any spring, will not "wear out" or get "soft". Most likely your splitting of lower bump stops are a symptom of too soft a bar, too low a ride height setting, crappy bumpers from China, or some combination of the three. If you are using anything less than the .870 (HD V-8) bars on the street, your bars are probably just too soft. .890 bars and a front sway bar, along with some good shocks, will add quite a bit of control to the motion of your front suspension, keeping it from bottoming too hard.