In the MGS Hangout area, add bar/cafe like what Tony said and add couches, some nice lights, some tables, and make use of that empty roof just beside the highway.
On the highway connected between DPD and Bohan, fortify the roads and add some glowing speed signs if possible, and at the toll booth area try to make it more, "policed", by that I mean add some of these cement barriers to the sides, and just make it better so police officers don't need someone to spawn barriers anytime they want to organize a traffic checkpoint.
Make use of the scrap yard just near the Lucchese HQ.
Remove the weedspot from the outlook park, it is very unrealistic for a criminal to plant weed in public park.. And add more weedspots in more common places that a criminal is going to plant at.
And literally change alderney, it is utterly useless. In the game story it was meant as an industrial area, and since most warehouses/oil factories/gun store already exist in Boabo or near the FIA. There is no use for such a mess in the map, except for the prison which is one of the places I like the most.
And please test if objects/entities cause lag/stutter/loss of FPS first
