First off, when it comes to spark plugs, I wouldn't get anything fancy for them, as they apparently have some weird behavior if you do, to the point of possibly accelerating distributor cap failure.

That being said, you can check for plug wire insulation break down as simply as misting them with water from a spray bottle while the engine is running. If you do this at night, you'll see arc paths from the wires to the engine wherever the insulation has broken down, if at all.

Depending on what you're describing as misfiring, it could be plugs, wires, vacuum leaks, or fouled injectors.
I know on my car, the injectors are the last point left to play with, as I've been in after the full ignition system, and the vacuum seals throughout when the engine was replaced. It shows as an occasional stumble, and various hot restart faults.

There was mention of using water spray to help find vacuum leaks as well, a while back. I'm not absolutely sure on it, but I seem to remember that the idle would slow when the water was sprayed in the location that the extra air was being sucked in, but it's been a while since I read that one. (It also seemed to be a safer route than the ether testing method, which was supposed to result in an increase in rpm when the leak was found.)

I hope this gives you something to think about, and best of luck!

__________________
-Josh
Testing the cheap Mercedes axiom, one bolt at a time...