I disagree. It can also be a good idea when your metagame tells you who is likely to win from the beginning. I tend to go after Jonts more than other players when there's such a choice to be made, because he tends to win the majority of games we play.
Well, I suppose that's true, but the fact that there can be a metagame that examines who is more likely to win based on previous plays is going to tend to turn me off a game.
Do you mean the fact that you can use this metagame to change your actions in the next game? Because any game is going to have a metagame where you know who the best player is from the start of a game.
As for trading, in the groups I play in for Catan, we pretty much always agree to not trade at all with anyone who is 1 point away from winning, or 2 points away from winning if he can get those 2 points with a single move. Obviously unless that trade happens on your own turn and would give you the win.
But yes, although I like Catan, it shares one of Monopolies biggest problems... the politics. People will help each other based on external factors, etc. Other games with politics, like Smallworld or even just any worker placement game, doesn't seem to suffer from this as much.