As with anything in life, people can work the system to their advantage. When you get promoted, you go up one level. When you get demoted, you drop down two levels.
So my advice is to just not worry about it until Sunday, and if you look up and you're in the top handful of places in your level for the week, kick it into great and play up aroom or two higher than normal and see if you surprise yourself.
I usually end up limping into Diamond I where I get blown out of the water by the guys who play Bellagio all day. Montreal is my comfort zone.
As someone else mentioned above, the reward is a fraction of what you would have to win to achieve it, so just ignore the weekly league if it ruins the game for you.