Best option for improving lap times is finding a good driver!
...or improving your skills as one.
I have the US M030 suspension. It's nice but as was mentioned, there are better aftermarket upgrades (I'm probably going to go the H&R route). Suspension upgrade will offer you the best opportunity to improve lap times (after improving driver skills, of course)
I imagine you'll do your own thing with wheels, so I won't mention that aside from saying my preference is a wider wheel (front ~8, rear ~10 - need to go aftermarket for this).
You can go without the PSM/traction control if you want but it won't really make a lot of difference and having it is better for daily driving and resale.
The glass rear window is a bit heavier than the plastic.
Aside from that there's not a lot of differences you can look for between model years (OEM) - at least nothing that will significantly impact lap times. Again, if you go to aftermarket, you can replace the exhaust system (headers back) for some improvement. Remap the ECU for a couple more hp. These upgrades will cost you, of course.
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