I wouldn't say it wouldn't improve their chances of winning the World Series at all, but it wouldn't change it enough to make it worth giving up top prospects. If you are going to give up top prospects, you need to acquire players that can help you longer than just this season and post-season. The only exception might be acquiring an ace starter. I think that's the only type of player that can boost your chances of winning the World Series enough where you might take the chance. Even then though, the Tigers never won it all with Verlander and Scherzer.