Just wanted to report on the results of replacing my OEM wires (of unknown age) with Magnecor 7mm wires. I opted for 7mm because I wanted the wires to still fit inside the wiring guides - if that doesn't matter to you, you may as well go with the 8.5mm for a nominal higher cost.
I bought the wire set from Apex Performance (apexperformance.net) for $90 shipped. In fact, the wire set is actually drop-shipped from Magnecor directly.
Before the change, the car actually ran reasonably well - the only real problem I noticed was a short stumbling when blipping the throttle from idle. I mainly wanted to change the wires after seeing the results in Grassroots Motorsports. I regularly campaign the car in autocross where every tenth of a second counts (yes, I have won/lost a class by as few as 1/10th on multiple occaisions) so I didn't want to be asking myself if there was some performance to be had.
Immediately after the change, nothing really seemed to change. The car still stumbled on throttle blip. However, about 200 miles later the car felt like it idled and ran smoother. The stumbling got much better. Pick-up seemed noticably better as well, however I also went to slightly undersized tires (195/60R14 which is 0.8" shorter than stock) so it's hard to say.
One negative (or positive?) thing - the cables are too short for the cable guides. Running from the plugs, the cables end up needing to take a shortcut from about halfway up the block and beeline to the coils.
Overall, I'm pretty happy with the investment.