Having read so many of these threads, I finally went ahead and replaced my coil packs even though I'm only at 45,000 miles. My plan was to keep the originals as spares. I ended up getting an unexpected performance boost, however...

I got the Hitachi "E" packs from ECS Tuning, popped out the old ones, and bolted in the new ones. Immediately I noticed my idle was smoother, and about 50 RPM higher than it was. I also noticed that accelerationg was smoother and a little stronger as well. It's been about a month now so if there was any initial placebo effect it's definitely long past.

I don't know if the "E" packs are simply better than the stock ones, or the stock ones degrade slowly over time. Either way it was a good upgrade.

(I carry all 4 stock packs in my trunk, because of multiple pack failure stories like this one :-))