Shocks, Struts, Springs and CC plates are what I call the "base" suspension components. They are the most important, and provide the foundation for the rest of your suspension upgrades. The bushings you have so far helped with steering response... and over all suspension integrity...
The next upgrades I'd look at are some rear control arms, or panhard bar setup. The rear of your Mustang is by far the most handicapped area of your car. Upgrading the rear end will improve handling, traction, cornering, safety, and many other areas of the suspension.
After that, you may want to look at chassis stiffening components such as Subframe Connectors, Strut Braces, etc. These items will help stiffen your car up, taking away the "5th Spring Effect" AKA your Mustang Chassis. They call it the 5th spring because there is so much flex and movement.
You can also install swaybars as well to help improve body roll and cornering... also tuning out understeer...
Printable Version
Suspension - 
