Let's just say this is a perfect world and the game works properly...no glitches/bugs....and you've find a modding genius who will make any mod for your game...what would it be?
For me, I think it'd have to be a mod for picture taking that lets you freeze sims in a certain position, so that you can continue to get the right position from the other sims in the shot without losing the position you already had from the other sims....if that makes sense...it would make life (and comps) a whole lot easier!