A quick note on the school of thought I follow:
Swaybars are good with softer springs -- they prevent lateral body roll, giving the car a sporty feel without a terrible everyday ride.
Unfortunately, they do nothing for brake dive or acceleration squat (both of which cause an increase of negative camber on the most affected tires -- decreasing the contact patch and lessening overall grip). To fix those problems, you need springs that are stiff enough to prevent extreme body movement.
Sway bars also limit the articulation of a suspension -- so if the right rear wheel hits a pothole, some of that force is transfered over to the left rear side (which means the right rear wheel isn't as free to absorb the bump). This is compounded when you run spring rates that are made to keep brake dive in check... So when you have stiff springs and swaybars and you start exiting a rough corner at full throttle, this can cause short bursts of broken traction (and once traction is broken, it is remains easier to slip -- google static vs kinetic friction).
Basically, if the car is a daily driver, running street springs and swaybars can give the car a better feel without annoying your girlfriend sitting shotgun... But if the car is being upgraded to haul ass on the track or backroad, I'd suggest limiting body roll is stiffer springs instead.