I do have to mention that a number of the "variables" you want to introduce have already been included into the Madden games. While I haven't played them in a while, I know that for the past several years they allow you to keep your seasons going forward (so you can have multiple seasons) and I believe you can download monthly/annual roster updates so you can have a more realistic experience (as long as that particular game is supported by EA). You can manage rosters/franchise and even set ticket prices, concessions, parking prices, etc. in some versions of the games to manage more of the business behind the game, which made it pretty fun. Most allow you to follow the draft (full version or speed through if you want) and you can make trades/acquisitions following standard league rules.

In terms of "random events" to different in-game actions, there is fatigue that does set in the more you play a player. In addition, weather, personal stats, and composure (usually through crowd noise) do make an impact on plays. For example, when it's rain/snow players slip, are slower, etc. Also, I lost my last Madden league season due to player fatigue (he fumbled at the end of the game!). They also implemented a "QB" vision option as well where one joystick is used to move a quarterback's vision around to find receivers. If you pass to a receiver outside the vision it increases the chances it will be dropped/intercepted/etc. I always hated it, because it really makes you concentrate on aiming down the field instead of avoiding the defensive rush...so while you do have a number of items you could improve upon the games, a lot of what you like are already built into some versions of the game.

Finally, I know once they started moving to Xbox360 and PS3 they developed a new engine that actively modified the computer A.I. to counter your skills. For example, if you are excellent at passing, the defense becomes better at blocking the pass while your receivers have a harder time making catches. I don't know the full extent (since I don't have either PS3 or Xbox360) but I know they were doing some awesome stuff with it.