Solstice GXP's have 2 braces that hold the bottom middle of the bumper cover to the impact beam. That's factory like that so no worries a bout the bumper sagging from the additional weight.
I would however strongly recommend cold bending a piece of 1/8" x 1" aluminum flat bar to match the curve of the bumper where the bumper cover is held in place between the headlights. If you look there you will most definitely see where the bumper cover is wavy gravy between the screws. If you push down on one of those pumps and watch neat the grills you will see the shape of the cover change and it will lift up. Those waxy spots are one of the causes of a large gap forming between the hood and the bumper cover.
The additional weight of the fascia/splitter is going to make the problem worse. You cannot use the factory screws wit the aluminum bar. #8 wood screws fit perfect. you are going to have to counter sink the screws and get the ones that have flat tops on them. I strongly suggest stainless steel as well. On my car I added additional screws one between each of the original screws in the middle. added another 4 screws. What the bar does is it holds the bumper over with a more uniformly distributed pressure across that edge and it doesn't allow the cover to get pinch spots where the screws go through it.
When adding the bar the 2 adjustments near the hood hinges may need to be adjusted up a turn or two. First time closing the hood close it slow and watch to make sure the hood doesn't drag on the added bar.
10 dollar investment makes the body panel alignment between the hood and bumper cover soooo much better.
this is what the problem looks like.
View attachment 120782
and this is what it looks like when the bar is put in.
View attachment 120783
see the difference?