First off, you don't want those "expensive" sparkplugs. The copper champions will work very well, and since they are cheap you can replace them every spring (or whenever.)
I would go along with Titans advice and do a full tune up. Replace the ignition wires, PCV valve, clean the TB with Ford TB cleaner, run some injector cleaner through your tank, etc.
If you run a K&N, you might want to clean the MAF too, as the wires can accumulate dirt/oil and throw things off. But you must be VERY careful. To find how to do this,
Click Here. Then click on "Cleaning MAF's wires."
Start with the cheap stuff first, then worry about trouble shooting more expensive parts.
BTW - Titan: your sig is almost a full page long. It's slightly annoying.