Do keep in mind that weekends are also more busy than weekdays, because a lot of locals come then.
I do whatever it takes to avoid weekends, but did get experience with a Sunday last year. (In September, of course--that's the only time we seem to travel.) The crowds were heavier, but manageable. The crowds for the parades were heavier than I was used to, but it definitely wasn't a crush. The lines for the rides were somewhat longer, but with FP's they were okay. Also, keep in mind that rides are probably going to down for refurbishment in the off-season.