Unless your name is Clark Kent or Diana Prince, there's only one reason to wear a pair of glasses—your peepers are in need of a little help.
And the glasses on display in Star Trek II remind us that Studly McStud Muffin James T. Kirk is getting older. He's forced to wear glasses to see things he used to spot without a second thought. We even get a pithy line from Bones when he gives the specs to his buddy, just to drive the point home:
McCOY: Dammit Jim, what the hell is the matter with you? Other people have birthdays. Why are we treating yours like a funeral?
Kirk is no longer a young buck, and the film isn't going to pretend that he is. This is an older man's tale, and the glasses make sure we see that clearly (glasses pun!).