I bought my Z before I had even heard of HPDEs. I started modding it like most folks do with bolt-ons like intake, exhaust and audio. My first mods were to get the Injen long tube intake and Hotchkis sway bars front and rear. I ran both sway bars while tracking for a long time until I learned I could cure my oversteer issues by going back to the stock rear sway bar. Now I just have the front sway bar set to the second stiffest setting out of 4.
I then added the HKS exhaust. The intake added some power on the top end and the exhaust just made it louder. It didn't add any power.
I then did a couple events and realized I needed to upgrade the brakes so I got the Stoptech ST40 BBK for the front.
I then did a few more events and realized I needed an oil cooler. So I got a 24 row cooler. I had to remove the injen intake to get it to fit. I figured it was more important to have a engine with less power that actually runs vs a dead engine that made more power at one point.
I bought a OS Giken LSD and 4.05 final drive gear in July of 2011 but the vendor did not honor the sale. I had to dispute the charge through my credit card company and after several months of waiting I got my money back. I decided to hold off on mods after that.
In March 2012 I decided to get dedicated track wheels and tires. I had started burning through my street tires rather quickly and I figured it'd be cheaper in the long run to pull the trigger. That meant I needed to get a trailer to pull my tires since I can't afford a tow vehicle. I went with a square setup of Enkei RPF1s 9.5X18 +15 and NT01 275/35/18. I got lucky and scored a South Sport Trailer from a fellow TJer. It was designed for Miata tires. He was kind enough to cut and weld it up to fit my bigger wheels and tires.
I also had to get new upper control arms to get more camber up front and to get the super wide tires to tuck under the fender. I ended up getting the SPL V3 upper control arm. I found that -2.5 degrees was the magic number for me.
My abs module and pump broke in October of 2012 and I replaced it in November. I ordered a new one from Nissan and I had a little trouble getting it. They had changed the part number from "47660 CF43A" to "47660 CF43B." I assume they made a change to fix the problem because I read about many Zs running into the same problem. Actually a good friend of mine with a red 08 Z (same year as mine) had the exact same problem, and it went bad within weeks of mine crapping out.