Can anyone tell me how sway bars and STB's will effect my ride quality??

Very little
 

... keeping in mind that I haven't actually mounted any on my Maxima yet :-)

An STB stiffens the chassis. While the existing flex may cause a slightly softer ride, I can't imagine that the stiffness of the STB will be noticed as part of the ride quality. After all, it only comes into play under harder cornering when the chassis is being strained - hardly the time when you are thinking of a smooth ride.

The SW-B should be equally transparent. It should only have an effect during cornering when the body is trying to tilt to one side. In the past, however, I have found that a thicker rear bar does result in a slightly stiffer ride - perhaps just due to the stabilizing effect it has on roll... keeping in mind that some degree of roll occurs even just going over a bump.

Bob

the STB, if designed correctly, will make the ride quality better. a stiffer, more rigid chassis will reduce the cowl shake. ride in a Lexus then jump into a Kia - you'll feel a difference in chassis stiffness :)

Strut braces and Rear bars
 

only reforce the solidity of the cars structure. -Meaning that ride will actually improve because more of the road vibrations are absorbed by the body structure of the car.
However, with the back end linked if one rear tire hits the pothole and thee other doesn't the rear rear of the car will dip a little more because its attatched and re-enforced to the other rear wheel -minor grip. Otherwise it vastly improves the cars cornering ability and fun factor even in slow turns.