It's not like Harris is a huge source of power either. Of the two, Winn is the better player, neither would be counted on for huge contributions, they'd be role players. If you get a chance to upgrade the position, it can do nothing but help. Winn is better in every statistical category than Harris both for his career and last year.
Harris is also tradeable and could be included as a decent piece in a trade somewhere down the line. Just because he's signed doesn't mean he's going to be here when ST opens. Any opportunity to upgrade any position should be explored. Don't get too attached to role-players or mediocre relievers.