I've had my LX since March 10th of this year. I've racked up about 6500 miles on it so far. I finally got an opportunity to test drive a Civic Si today.
Here's my observations of the differences...
The Si has a good exhaust sound. It's not loud, but it has a nice pleasant sound to it.
The Si has far superior steering. The LX has ZERO feel and feedback. The Si has a much better feel. Too bad the Si uses an all electric power steering system that'd make a retrofit impossible.
The Si has superior seats to the LX. Much firmer and more supportive.
The brakes in the Si are much more responsive and the pedal feel is more linear. Like the steering, I hear that upgrading an LX to Si brakes is nearly impossible. I know there are plenty of BBK's out there, but nothing beats the easy availability of spare pads and rotors of OEM on a car that gets 40K+ miles per year.
Suspension wise, the Si is far superior also. None of the "floaty" pillowcloud ride like the cheaper versions have. The stock LX suspension purely sucks. I added the Si swaybars at 1600 miles, and that ain't enough. I'll be getting the springs/shocks within a week or so. The Si achieves a good balance between ride quality and comfort. To be honest, I was expecting something much harsher and darty. I'm anxious to meet up with my seller to get the springs and shocks now!
The transmission in the Si had a much crisper shifter. It just felt right with its crisp chort throws.
The difference in the engines was less dramatic than I expected. It seemed a little more peppy and it certainly sounded better than the LX. The salesdude kept telling me that I wasn't driving it right. He insisted that I rev it hard. So at the next stop, I ran it up to 4000 rpm between shifts. It's stronger than the LX, but he said that it had to be revved much higher to feel the difference. So I stopped and revved to ~7500 between shifts. IT REALLY WOKE UP!! When you spin it up, the Si will scoot!
Is it worth the price difference? Yes and no. With my long history of low revving cars, it's hard for me to let something wind up like that, but if I could go back in time, I'd have the Si instead of the LX.
I inquired about swapping cars with him. I was hoping to swap for maybe $1500-2000 more than the price differential between the two models. My car is only 6 weeks old afterall. They wanted $8945 before the taxes and other BS hidden fees were added. The Si is the superior car, but it ain't $10,000 better.
Congrats to all the Si owners! Y'all bought the right car. I tried to go cheap...
Rawhyde