cost isn't as bad as one would think for that list - though it did cost a fair amount, I've done it over time, engine wise since 2006 (winter) when we started the build, and completed it in summer 2007. So, it's amortized over time, as money/time allowed. I have owned many FI cars in the past, and had never done a full NA setup, and since I utterly love my Z, I just wanted to try something new and learn in the process. Overall, out of all the cars I've owned/modded and still own, this is my favorite. I absolutely adore it!
currently, lots of changes have been made from that setup
Cosworth manifold
Haltech with Racepak dash
converted to throttle cable from drive by wire, using 75mm throttle body
larger intake setup (custom, though we'll be making changes in the future)
new pumpkin with Quaife LSD and custom 4.3 final drive
Peak power went up a few, peak torque went up about 10 ft lbs now from before thanks to VTC mapping (which we were not previously able to do on the UTEC)
As for the supercharged cars, I can easily walk away from one...literally. The s/c kits on a Z work great - HKS, Vortech, etc. Easy to fit, work great on a stock engine, reliable, and put down nice power. However, these are on stock engines, so max rpm is limited to stock redline. My car redlines currently at 8400, and makes power all the way to the end. Torque stays nearly flat to 8k where it now trails off just slightly at redline. So, while the Vortech etc car makes a higher peak number, I have nearly 2000 rpm more, per gear, of peak power available to me. Coupled with the shorter final drive gears (previously 3.9, now 4.3) and the car has that power at immediate disposal, without any "spool' time (the Vortech kit in particular tends to make its power higher in the rev range, HKS is more of a mid range setup). The car is more akin to driving a GT3 now in terms of how/where it makes it's power, than it is a Zed
There are some changes we plan in the future as well to try to eek a bit more power out of her. The next step really would be a more dramatic cam, and possibly a different header, though I really want to just explore the limits of the current setup as I've very happy with the overall performance, and it's been spot on reliable now (15k miles and counting)
As for the highest NA power without doing internals, the 07 + will always make more than the previous cars due simply to better overall internals, more aggressive cams, etc. Peak power on a DE (revup or non) is realistically limited to around 280 whp on a dynojet (other dynos may read differently, lot's of variables involved)