If your car has more than 75,000 miles on it, you might want to do some maintenance on it before upgrading anything that'll increase its power. Even without upgrading, aggressive driving, high rpm shifting, and high speed driving can cause problems with an older engine.
Before
Check your engine's compression. If it's low, pushing your car to the limit may worsen it's condition.
If your timing belt or water pump hasn't been changed yet, do it. Both should be changed every 60,000 miles, but with casual driving, you can get away with a few thousand more miles. Pushing your car to the limit may cause one of these to fail. If the timing belt brakes, your engine's pistons will crush the valves, causing massive damage. A timing belt and water pump from Ford will cost $200-$250, or you can get them from a local auto parts store for a fraction of that.
Replace the valve cover seal. For about $15, it'll keep you from having problems in the future.
Clean out your intake system. For about $30 and a few hours worth of work, it's a very worthwhile improvement. As you add on the miles, dirt and oil can build up in the intake manifold. Cleaning out the system will keep the air entering the engine cleaner, which is overall better for your engine. I did this to both my Probes after 100,000 miles. The intake manifold and EGR valve were filthy. Afterwards, there was a healthier sound and more powerful feel. This is highly recommended.
If there is oil in your intake system, it's most likely due to excessive blowby. To keep the oil from entering the intake system, remover the breather tube and place a filter at the end. Remember to plug up the connection at the intake boot. Breather filter installation instructions can be found in the Do It Yourself Upgrades section.
After
After you begin to upgrade and/or you start driving harder, you'll have to replace some seals. With the higher engine speed and oil pressure, the old week seals and gaskets will begin to fail. Not all of them will, but most likely the front crankshaft and camshaft seals, the oil pan gasket, and the transmission pan gasket. Their not expensive, just a bit time consuming to replace.