Ditto on what the others said.
Plus, unless you are in a keeper league, focus less on a player's upside and more on his track record, at least early in the draft. League championships are rarely won in the early rounds but they can be easily lost. Go for proven reliable players early.
Most championships are won in the middle rounds. There is usually very little difference in most rankings when it comes to the top players at each position. Finding the undervalued guy in round 6 that is going to have a breakout season can carry you to a title. This is where to spend your time and identify players that everybody else is down on but is primed for a good season. Like Drew Brees last year.
When you get to the late rounds, that is the time to start thinking about players with a lot of upside but are not proven. You can't sleep too long on some of these guys, but there are always late draft picks that are set for solid seasons. Like Tony Romo last year. Not that he was Carson Palmer or anything, but he was better than half of the other QB's.