There's nothing interesting about the quality of light
What's "interesting" about the quality of light. It can be beautiful. That's what counts.
3) I can place a SB lot closer to the subject.
I can agree with the other points, but not this one: A shoot through umbrella can be about as close as a SB IMO.
One advantage to an umbrella: Keeps you and your equipment (about) dry when you get caught in the rain 
Will larger umbrella be a good idea?
Having options is always good.
Why would you want a larger umbrella?



