When the Mets won the World Series in 1986 - MLB rosters were down to 24 players.
It was also a different time. Starting pitchers went deeper into games. Relievers went longer, too.
A team could get away with 14 position players and 10 pitchers.
But that didn't last for long. It was soon back to 25 players.
Since then, the role of the bullpen has changed. Pitchers didn't go as deep into games. There were the lefty one out guys. Teams regularly hold 12 pitchers. This leaves 13 position players. Less than in 1986. This leads to thinner benches. It's led to guys who are purely pinch hitting specialists (like Rusty Staub) becoming a rarity. There simply isn't a roster spot available for it. If you're on the bench and can't play the field in more than one position, there's no use for you. If you're not going to be a full time DH in the American League, there's no use for you.
With a 26 man roster - Vlad Guerrero would have been signed. Hideki Matsui would have been signed. (Some may argue with that, but if there's an extra position player spot - why not take a flier?)
So here's my proposal. Expand the rosters to 26 players. Have the purpose be for extra bench depth. And to make it "fair", designate a specific roster spot as the "26th Man" - which will be a player at the minimum league wage. It will keep the owners happy by not jacking up payrolls more. It will make the players union happy by adding another 30 full time MLB jobs (not to mention racking up service times to additional players). A team could either add a veteran specialist looking to play for another year that isn't getting signed elsewhere, or they could give a young, versatile player an opportunity that wouldn't have otherwise had a chance to prove themselves and at the same time free up a spot for a veteran specialist.
Let's go to 26 men.