I own a 2006 civic si.
I really like the "lacking" interior. I wanted the car for the 'engine," not for the interior. I didn't want leather anyway. and the car isn't lacking compared to all of the competition. It's cheaper than something like the GTI Mark V, and it looks way better. for the money, you're getting a great car.
I nearly tied a Solstice GXP the other day. I have the original stock tires still- not the summer tires. My front end was still at his door when we hit 70. Maybe it was the driver, but that car had 50 or 60 hp on me. It could have been any number of things, but he probably should have smoked me.
I love my si, and I haven't for one moment regretted buying it. I think that both the sedan and coupe look much better with the factory aero kit- but the sedan looks especially bad without it.
the LSD makes it a pleasure to drive, and in my opinion, it's much more attractive than any RSX ever was.