Lens hood reduces stray light (this is a good thing) which causes flaring and low contrast. In daylight you can still benefit from very fast shutter speeds which increases the chances for razor sharp in focus areas.
If you want a lens that focuses really well in low light then use the 50mm f1.2 L OR get a flash (430) but not to light up the subjects, instead just use its focus assist light which is excellent and will allow you to focus in next to no light.
Not sure. I sold my 50mm f1.4 (the f1.2 L is expensive) and I don't own a f1.8. Will try and see whether I can get my hands on them and will let you know.