I had one for about 80,000mi. It was a great car until I removed the balance shafts. DO NOT DO IT. unless you are building the QR25DE for an all-out race application, leave the damn things in there. You will not feel the extra 8hp. What you WILL feel, is more vibration, and EVERYTHING will be louder. It's not like Formula 1 car loud, but it's annoying.

I LOVED that car until I did the balance shaft removal (BSR). Then it got old really fast. I also had motor mount inserts, which obviously amplified the problem...but I consider the $40 (and removable) motor mount inserts to be much more beneficial than the BSR, as the inserts will almost completely eliminate wheel hop.

Definitely replace the header. Definitely get a CAI and a decent exhaust. I had an AEBS header and Thermal R&D exhaust, and the car was actually pretty quiet. Until I did the BSR, and then it was more obnoxious. Lightweight crank pulleys are nice (but kind of a pain to install). I was also able to gain 7whp with an SAFC2 tune. I had an 03, which I think is still the best year (02s had lots of issues, 04+ were butt-ugly IMO).

The only things that ever went bad on the car were the MAF (killed by vibration from BSR), and the ECU (recall). Otherwise, I averaged like 25-26mpg in the city, autocrossed and drag raced the crap out of it, and had a blast the whole time. I've actually been thinking of grabbing another one as a DD.