Mac, you've got it exactly backwards. Making the front bar heavier, relative to the rear, will generally make the car understeer. Likewise making it softer will make the car oversteer. A stiffer rear bar, relative to the front, causes oversteer, and a softer rear bar makes it understeer.
This relationship between bar stiffness and over/understeer is well understood by anyone in any type of racing that involves turning corners. Basically, you stiffen a bar to make that end of the car take more of the load. You're asking the outside tire at that end of the car to take more of the cornering load, relative to the outside tire at the opposite end of the car. That makes it break loose sooner. So more bar, at either end, has the effect of reducing traction at that end and increasing it at the other end.
Increasing spring rates has the same effect: more spring means that end takes more of the load and therefore gives it less traction and gives more traction to the opposite end. For equal reductions in body roll, a heavy spring will load the outside tire less than a heavy sway bar. The other factor is that sway bars take away the independence of the suspension; hit a bump on the left side and the right side feels it too, and vice-versa. Heavy springs are the preferred way to control body roll as a result. Sway bars are generally a tuning device to balance the car once it's sprung correctly.