First, I am neither a Patriots' fan nor a Patriots' hater; as for Bill Belichick - well, all I know is his public persona; I hear that those close to him feel like he is a person worth knowing, so I'll leave it at that.
The answer to your question, is, I think, "Yes, Bill Belichick needs to be let go." I know that you think that Spygate has been overhyped, and you're probably right about that, but the fact is: the man tilted a supposedly "level playing field" towards him and the Patriots. Does that "taint" the Superbowls? Well, forgetting the games that led to it, in the first one the Patriots were heavy underdogs to the Rams. That they beat them is not the issue; it's now HOW thaey beat them that has come under scutiny. When you think about it, unless they are blowouts, all football games in reality come down to a relatively few plays. Now, if the Patriots - or ANY team, really - have the advantage in knowing what is coming at them in those key plays, then they have an unfair advantage over the other team. So, I would say that yes, that affects the outcome of the game. Who knows who WOULD HAVE had the upper hand in those particular plays?
And who knows if all of their playoff games BEFORE the Superbowls were on the up-and-up? Who knows if the even would have made the playoffs in the first place but for two or three key games during the year? Those questions would mean that yes, while it might now "taint" them as a team, it DOES taint them as one of the best ever - just like steroids have done to Barry Bonds and Roger Clemens; botth men were good ballplayers before their insatiable desires to "be the best" led them down the steroid road, and "tainted" their accomplishments.