I'm not sure about what benefits it could bring. Most people who are in favor of malls being closed don't visit them on Sundays anyway. I think it's a bit naive, though nice, to think that this act somehow encourage people to spend more time with each other,I mean this is the main reason I usually read.
The only people that this might not be true for are the employees.
I agree that it's not <em>necessary </em>to be open, and having a weekday is not the same as having an extra day of weekend, because most events happens at said times.
There are some employees,especially part-time workers and students,who actually prefer to work on Sundays,though.
I think it would be okay to have malls open from 8-14,it's kind of a half-way between the extreme.