what i meant by that was that the suspension enables the car to corner incredibly hard, but the tires cant make it stick. i once (unintentionally) 4-wheel drifted thru a corner b/c the tires let loose...zero body roll, all the tires planted...they just slid...if i could have some racing tires it would be insane
the panhard bar controls lateral (side to side) motion of the rear axle...keeps it planted firmly and straight...its DEFINITELY worth getting, period. the understeer is mild, but thats only because my car doesnt have the power to break the tires loose at speed and create oversteer. although, the tires i have suck and can cause the car to tail out...
in fact, in situations where i was always able to light up the tires w/o a problem in any of my past vehicles...well lets say i embarassed myself a little because everything was so well hooked up.
as with bracing, if you are gonna do it, do them all. strut tower, k member and subframes. the strut tower brace and k member brace kinda go hand in hand, but when you have them all together its AWESOME
only downfall is after you have all this done, you give up ALOT of ride quality...but after you carve the first few corners, it becomes worth it...
next upgrade = brakes!