Dave Myers has written the following article on Favre for the LaCrosse Tribune, which discusses Favre's legacy and the things he brings to the table which go well beyond his future Hall of Fame resume. The author brings up some points that I haven't seen outlined elsewhere with as much clarity.
Here is the link to it: http://www.lacrossetribune.com/articles/2009/07/02/sports/00myers.txt
While Myers main audience is in Wisconsin readers, his words have a much broader context and interest. His main points are that Favre wants to play for Minnesota, the Vikings want him to sign him if healthy, Favre's legacy belongs to Favre, since he's the one risking his body in continuing his career, and that Favre brings with him the opportunity for increasing revenues for the Vikings and the NFL in terms of ticket and jersey sales and publicity, which reminds us that it is called "professional football" because the NFL is a commercial enterprise and not only has to bring a sport to the fans which they will enjoy, but must also make a profit in doing so, in order to continue the operations of all its franchises.
Whatever Favre can and cannot still do between a kickoff and the end of the game, Favre is important as a means of making money.
Without income, there are no future Minnesota Vikings.