Personally I think our roster is pretty well set. I think a lot of people on this board forget we have a great athletic back up to Paul Pierce in Marquis.
While part of me would like to hold onto Sheed's contract for a later point (though I don't know if the NBA would let us do this), I disagree with your thoughts on Quis. He's too big of a health risk to rely on, and Paul Pierce can't play similar mintues to what he did last season.
Here's games played throughout his career: 54, 54, 74, 45, 62, 60, 56
If you could turn injuries off, Quis would be enough.