You will not improve "picture quality" by improving signal strength or quality. Digital is all or nothing (unlike analogue signals which deteriate slowly)- with blocky pixellation etc on the borderline. If you are not suffering from this you cannot improve picture quality
Absolutely true, but a higher signal level will give a greater fade margin in bad weather.
I've just moved to a location literally on the south coast (we can look across to France on a clear day).
Despite having the Sky dish professionally aligned, we regularly lose satellite reception in the driving rain that we've been getting lately.
My new neighbours confirm this is a well known phenomenon.
So, I've just invested in a Zone 2 dish (really meant for the north of Scotland) in the hope of getting more reliable reception.
Time will tell...