A recent Los Angeles Times has an article on exercises and technology which are helping baseball players see the ball better. A sample:
The device is a high-speed pitching machine that fires specially marked tennis balls at speeds up to 155 mph. Players try to read the markings as the ball flies by, an exercise intended to improve both focus and concentration. The Kansas City Royals, Seattle Mariners, Chicago Cubs, Cleveland Indians and the Olympic champion U.S. women's softball team have experimented with the ocular machine.
Another promising advance is the amber-tinted contact lens. Baltimore's Brian Roberts, Dodgers minor leaguer James Loney and the White Sox's A.J. Pierzynski are among dozens of players who have experimented with the lenses. They are designed to filter out specific wavelengths of light, cutting down on glare and making the ball appear more clearly.
The benefits resulting from the performance enhancements would likely exist regardless of whether players had the right to free agency. Fans want to watch play of the highest quality and are willing to pay for higher levels of absolute quality, all else equal. So the performance enhancers create extra quality and, therefore, extra revenue generated by the player. The question is who lays claim to the increased revenue?
Free agency gives players a right over where they play and, indirectly a claim to revenue generated by their play. The reserve rule gives that right and the claim to revenue to teams. So under the reserve rule, teams would end up largely paying for enhancements. Under free agency, players end up paying for them.