Reds defense improved last year. Fielding percentage went from 979 to 984. I know that's not the only relevant stat, but it is an indicator. I think the infield got better with Gonzo and Kepp at shortstop and with EE's improvement.
The outfield, however, remains defensively challenged with two offensive players, Dunn and Griff (at this stage), in the corners. I think getting a plus centerfielder is important. All the Fielding Independent stats being floated around show that Reds pitchers need more help from the defense.
Cameron is the obvious guy for centerfield. If there's someone else I'm missing, I'm sure posters will say so, but I think the Reds would be helped enormously by a defensive centerfielder.
Dickerson is another choice, but he doesn't seem to have a starting player's offensive credentials. Maybe as a backup.