We always recommend replacing the old rubber bushings with our new polyurethane ones. Many times, front end wandering or shaking is due to worn-out bushings. If your Bronco is still running 30 year old rubber bushings, it's time to change 'em. Our polyurethane bushings are black graphite impregnated for quiet operation. How often do you need to replace polyurethane bushings? C-bushings last the longest of the bunch, and you may never need to change them (unless you change suspension heights). Strut/radius arm bushings should be checked from time to time. Cracking can be caused by over-tightening and four wheeling. If you see cracking, they should be replaced before they fall out.
The track bar bushings are the weakest of the front end bushings and need the most attention, considering you've got the whole side-to-side motion of the front end being controlled by these bushings. The upper one wears the quickest. Shaking of the steering wheel is the first sign of a possible trac bar bushing problem. It's a good idea to carry extra trac bar bushings, especially if you're into off-roading.