The bushing upgrade is simply removing the factory soft gummi bear rubber and replacing it with high density urethane. This will drastically improve shifter feel and accuracy.
The factory STS retains the stock shift lever and rubber bushings, but has shorter linkage between the lever and the trans.
You definitely want to entertain the idea of getting the bushings.
You may also want to look at doing a 'super short throw'....adding an after market STS lever (like the kartboy) to the factory short linkage, and adding the bushings.