In my keeper/dynasty leagues i of course value young players over old, but i try to be competitive every year. If I can trade a top prospect for a guy to help me in the stretch run (and i have a realizable chance to win) i make the trade even if the young player has huge upside. I feel comfortable enough in my knowledge of the minors to find another prospect to replace the guys i trade. Obviously i won't "give away" young players, but i am one or two pieces away from a crown i make the move. For example in one h2h league i was getting killed in saves every week, so i traded Brandon Wood for Izzy. I am not going to keep Izzy, but he grabbed a couple of key saves in September and helped me to the championship game (and a finish in the money).
"I do not think baseball of today is any better than it was 30 years ago... I still think Radbourne is the greatest of the pitchers." John Sullivan 1914-Old athletes never change.