Those are two fairly unrelated issues. In any case, the pinky is usually quite strong naturally. Besides the thumb, this is the only finger that has powerful muscles in the hand. As tds eluded to already, it is more a matter of proper technique rather than muscular strength. Like any other finger, the pinky requires proper alignment with the forearm when it plays. Focus on this type of movement instead of tryng to build strength. What kind of strength are you actually referring to? Is it the type of strength that lets you trill with the pinky, or the type of strength that lets you play fortississimo with it? Whatever the answer may be, muscular strength has little to do with either one of those.
WRT the hand span, it may naturally increase a bit, but more likely than not, you'll be "stuck" with the span you already have, give (or take) one or two notes. You could do stretching exercises, but better not force things. Stretching the hand is a very tricky business.