Just a few words. I find 11 players is the sweet spot for me. Every time I try to carry 12, that 12th player just doesn't get the playing time he needs.
Also, about Stamina: I think there are two ways to deal with the stamina issue. One is to train Stamina or buy players with high stamina, but the other is to use substitutes and have high quality subs. If no one is being asked to play a 48 minute game, having low stamina doesn't seem to be too bad.
That, in turn, leads to 2 position training. By rotating starters and using subs, I can get 3 guys 48 minutes in my league games, without sacrificing how I play, and then get 2 guys 48 minutes in my friendly (by playing them for the whole 48). If I did 1 position training, I'd be forced to either train 2 players, or have everybody doing the whole 48 at a significant hit in performance -- or I'd have to train stamina, which would cost me whatever gain I was getting from 1 position training. If you can dominate anyway, like the Dawgs, it's worth it; otherwise, winning games is connected to making money in this game, and money lets you buy better players and keep better players.
Also, I agree with the assessment that Wondrous is much better than prolific when selling a player. However, when factoring in the cost of the players salaries, etc., I don't think it's 500% better than prolific for purposes of actually playing that player. In fact, I think there are diminishing returns with each level, in terms of how your team plays, once your player is just slightly better than his opponent. And having a few players be Wondrous, while the rest are less than prolific, gives you less flexibility to play different offenses than a more balanced team would, which has advantages as pointed out earlier. And having a Wondrous guy is more expensive than multiple prolific types salary wise.
That was more than a few words, wasn't it? Great thread, though.