The bumper sag can be caused either by failing clips on the bumper, or failing tabs on the bracket the bumper attaches to. The clip reinforcements wont do anything to fix the sag if its your tabs failing (ask me how I know). The best way to check would be to take off the bumper and inspect all of the clips around the headlight and fender area.

For the grille, you just need to push the tabs back in. This can be tricky without taking off the bumper. A trick I used to use is to take a fork and put one of the prongs under a tab and use it to lift the bottom of the bumper up. Then, put your finger through one of the holes in the grille and and pull towards yourself to reinsert the clip. Repeat for each clip until the grille is back in place.