Suspension was one of the last things I have done to my Corolla, after air filter, synthetic oil, and general tuning of engine to specifications, but looking back it should have been the first.
My advice: suspension upgrades are worth it! It is no good being able to go faster if you can't corner or brake very well. A suspension upgrade, including stiffer shocks and heavy duty springs will enable you to both corner faster and brake more effectively.
Lastly, lowered springs do not affect suspension performance! Do not believe everything you read. What is important is the spring rate (how much it compresses when a set force is applied) being matched to the shock absorber.
Lots of people say that Pedders are not that good, and recommend exotic brands. I have used Comfort Gas shocks (a nice compromise between road holding stiffness and comfort) and Pedders heavy duty springs, and have no complaints.