Peeps who’ve added insulation to attic- what kind of improvements may I see?

House built in 2006 with original insulation. Only insulation is the original pink fiberglass rolls that are laid between the 2x4s (joists?). House has no shade from the west so late afternoons the house gets pounded. Original double pane builder grade windows

HVAC is a new system and performs pretty well, wondering if it’s worth adding blown in cellulose

Also considering DIY vs paying a contractor, about to get quotes tomorrow to see if it’s worth it

I know there’s other factors like how leaky the house is etc