Yes, 2.8 is good for low light. It will also help to keep your shutter speed up for sports. But, if you are consistently shooting low light then 1.8 or below is better. I still think that the 70-200 2.8 is your best bet as it will cover both candids and sports which are two of your top priorities.
i am looking into the 2.8 myself and would prefer to the the non-is (eventhough i know the IS is a huge benefit)
what is YOUR personal perspective on the 2.8 IS vs what you have?
if possible (through pm perhaps), could I also see some shots of your 2.8 in low light settings? perhaps those candids you were talking about.
do you shoot it handheld?