TRACKBAR, anyone here run one?

Del, you are missing the effect of the change in the roll center with the panhard versus the stock spring mounts. These cars tend to transient oversteer badly when thrown hard into a corner, due to the higher rear roll center of the spring mounts, and the panhard rod will help reduce that 'tail happy' tendency a lot. And, I can promise you that the centering consistency of the panhard rod will be far, far better than the stock springs. The small lateral movement of the panhard rod is a consistent movement; the opelgt.com link below discusses the left/right tendencies more. The watts linkage eliminates this but is a lot more complex.

OP, no the rear sway bar may be needed. With the roll center lowered and less oversteer, you will be putting a front anti-sway bar in (if you don't have one) and then see where you are with oversteer/understeer. The overall car's roll resistance will be a combination of the spring rates front and rear (t-bar and leaf) and the 2 roll bars. If you want it to corner flatter, you add front and rear bars and adjust the stiffness between the front and rear bars to manage over/understeer. Of course, since you want to keep expenditures minimum, then you don't want to buy a variety of sway bars; the panhard rod, if adjustable in height, allows you to tune around that some.
BTW, the adjustability probably is the one thing to jettison to reduce complexity, but it might save a sway bar change.
BTW2 For auto-x, the transient over/understeer will be very important, and that has a lot to do with the shocks. So you can set the static under/oversteer but you will still have shocks to work on.

And, yes, that is why the NASCAR guys are doing this, with the vertically adjustable chassis connection to the bar/rod.

Don't use tie rod parts for this. Use a 3/4" (1/8" wall, it's too heavy but can be threaded for a heim joint in one end) mild steel tube, weld on one tubular end for an eye and use a poly or rubber bushing in that, that fits over a stud on the axle connection (which can be a strong stud welded on the lower spring plate, and then put a 5/8" threaded heim joint in the other end that fits a bolt in the chassis mount so you can get it centered. This link, which I forgot to provide above, is a really good thread on these details.
http://www.opelgt.com/forums/perfor...-panhard-bar-roll-centre-geometry-racers.html

But the points on weather proofing are well taken; the heim joint is not weather proof.