I just collected a bunch of Gary Sheffield game used bats (from late in his career) and I realized he didn't sand down the handle of his bats. They're like war clubs. Also, a Louisville Slugger (C324) of Jack Clark's last year in Boston reveal a "whiffle ball" thin bat I'm guessing for bat speed. This information would not have come to me unless I handled these items.
Has anyone else found out interesting things about a player from collecting game used items?