Short answer, no.
Long answer noooooooooo. ilvl is most important, as long as you're wearing some kind of ilvl90 stuff, it doesn't really matter all that much. min/maxing helps your raid of course but is it necessary in this game? one can argue only for twintania, and even that is debatable. Min/maxing stats is always helpful, but never make or break. Min/maxing spell timings is often unnecessary and failure can lead to a wipe. Many tanks are 40-50 points over accuracy cap with their gear at some point and theres basically nothing they can do about it.

edit: I am a tank on turn 5.