Just buy cheap, parts store ignition components, and only replace things if something breaks. Stock ignition parts are good for 300+ horsepower and 200k+ kilometers, and "upgrading" them won't get you any more power. Not even 1hp. Always use NGK copper plugs with turds, but since you already have the iridiums, keep them until they fart, then buy coppers.
If you actually want to go faster, a manual is your best bet. It's probably cheaper to sell the car and buy a manual than to swap.
A complete exhaust would be your next best bet, but that's $500 (or more) and will get you maybe 6hp. You won't feel much difference, and you'll still be running high 16's in the 1/4 mile, slower than a lot of cars out there.
The mod that will make the biggest difference to your everyday driving will be tires and rims. Lightweight 15" or 16" rims (under 13lbs a piece) and sticky summer tires will make a world of difference.
I've been there and done that, just trying to save you money