[MyShibbyEco]

I'm going to be the first to agree with David1 in that this will have negligible effects, and usually doing something like this is a mask for other possible problems. I do commend you on the write up and good picture taking, though.

this is a totally different car then the cruze but we did a baseline on a 350Z equipped only with the Blitz intake(which IMO makes an ants d*ck worth of difference anyway).
Baseline was 238.2 RWHP and 228.6 lb ft of torque. we added only the Hyper ground wires and saw 242 and 231 respectfully.
I know the difference is small and is even within an allowable margin for error but it seems to me for $25 the grounding kit is good for a few ponies!! we also noticed a better throttle responce and smoother idle!
after setting up a bet with my co-worker we disconnected the ground kit and found we were back to 238.6 and 229. reconnected it and got 242.1 and 230.9. and i made $50 hahaha

Was this all in the same day, under the same conditions, with the same driver, same engine temperature, etc? Something as small as 0.5*F and/or 2% humidity change is enough to cause a 4 HP/TQ difference.

It's not a placebo exactly. Certain problems can arise with too much resistance in the frame. For example, in my camaro, running a ground to the engine, frame (front) and frame (back) helped the fuel pump because the stock wires were too thin gauge and the frame had too much resistance.

Your Camaro is also 25 years old. The metal frame has had time to rust, change properties, corrode, etcetera. I will agree with the small gauge wire, though, but that is also something most cars have in common.

I wouldn't be so sure it's a placebo. If you've ever tried to jump a car by putting the negative jumper clamp on the frame of the working car you'll discover it's much harder to do than if you put the negative jumper clamp on the battery directly. This is because that while the entire car is "ground" level there is a lot of resistance between the various parts of the car and the battery's negative pole. Electrically this means the car itself isn't at true ground, just near enough to it for most purposes.

I would argue that a battery has a better conducting connection than any part of the frame (not to mention the frame does not always lead straight back to the battery), and has little to do with the frame not actually being at ground.

Personally, if I have an electrical problem with my car I start my checking for corrosion on all grounds. If they all check out I look at any electrical components that may be drawing inappropriate amounts of power. If you have a grounding problem on a new car, the first solution should not be to add more grounding points, let alone do so without checking if more ground points are necessary for your application. Also, just my opinion, but 4awg is overkill. A truly good grounding set up would be a car that runs all ground points back to the same spot, not adding more in different places.

These are all just my opinions, so take with a grain of salt.