WAAS should give way more increased sensitivity.
Think of the satellites tracking you from space and how accurate they can be - 15 meters or so.
Now we add the assistance of ground based stations that help the space based and bam! We should see accuracy as close as 3 meters.
WAAS should make your position almost 5 times more accurate. I'm not sure how disabling this is going to enhance accuracy..
If it were me I would leave it enabled.