One trick I've started to employ is to actually zoom in on my browser to a comfortable level as well as zooming in on the map, as it's a little easier on the eyes.
If I'm using the closest zoom on the map them two clicks on the up/down direction button will take me to the next section of the map up/down and when I'm finished the current "column" then three clicks on the direction button left/right will take me across to the next "segment" of the map to the left/right, so I use this to search the map systematically.
I start at the top left corner and effectively "snake" my way across the map by going all the way down, moving to the next "segment" to the right, going all the way back up and then rinsing and repeating until I've scoured the entire map. Found a Gift Card, SKS Carbine and a Flare Gun (one item each time I've searched across map across several hours).
Edit: 7/10 upgrades on Awareness
I've been employing this exact same strategy with 0/10 merits in awareness, and I've found a grenade, Ruger 22/45, and a lollipop. Its more items than I have found in the last 2-3 months. I go three clicks to the right when I transition to a new "sector", is that about what you're doing, or are you being even more cautious by overlapping your search?