Would installing the Stage 3 2 pass end plate give any gains on an otherwise stock engine ( GMPP exhaust ), or would it just run a little colder (I guess a little safer) ?

That is all.

 

It would just make your Intake temps lower which makes it more resistant to detonation(knock). You can add more timing to get a bit more power if you have HP Tuners.

 

^^^exactly.

There are really no noticable power gains unless you retune the car. And even that isn't a whole lot.

 

Yea agreed,

with my limited knowledge of cooling systems, i understand it to be an "anti-heatsoke" measure taken to allow moderate-heavily modded cobalts to perform repeated drag races or long autocross events without losing horsepower due to heatsoke.

Putting it on a near-stock cobalt is definately not a bad idea, but in all honesty is not the best mod for the money in your case.

Its more for a decently modded guy that is looking to make his car more efficient and consistent.