It sounds like you've answered your own question. WHY do you feel like it's important to improve your range? I'd assume it would be to get to more balls; and be able to square up to balls that are at the edge of your current range. WHY would that be any different at 1B? Getting to more grounders would cut down on opponents' hits AND keep more runners from advancing. If you could prevent the opposing team from scoring thirty runs how would that be any different from adding thirty RBIs to your statistics?
Before we make a major investment into an extension for Mark Reynolds, or even consider picking up his 11M option, we should get his word that he will work hard this winter on improving the weak areas of his game. He clearly worked hard last winter on his weight. I'd take his word that he'll work on his range and hitting to the opposite field.
Shortstops are expected to cover alot of ground. First basemen are not. There aren't many instinses where you need to take more than two steps to get to a ball. He has a great first step. And I believe he has a good second step as well. Please cite examples where he couldn't get to a ball he should of if he had a better second third etc step. Because I think you are basing it off of range factor.