Are you seriously trying to finish in the middle? The whole point of fantasy baseball is to try to win your league. Have confidence in your abilities and try to win!
I can see some times when it makes sense to aim for the middle. For example, I just took over a keeper team that was a real fixer-up'er...I traded a lot of my picks to create a VERY solid list of young keepers, traded some more picks for pick upgrades in 2007/prospect draft upgrades this year and already had a below average draft when I took the team over. My first pick is in the 8th round and we only keep 6 so aiming for the middle makes a hell of a lot of sense for me...it's not selling myself short - it's just being realistic.
That said, if there are no keepers yet and no one has an advantage as far as more picks in earlier rounds then the heck with that strategy. If you don't think you can finish in the top 12 out of 15 then you really need to play in a different league to hone your skills a bit first anyways.