I second JF – a year in sem is not necessarily about the classes, it provides a very good foundation for the rest of your life. Spending a year living in a dorm with other girls is major education of itself.
I was also born in a solid frum home, and I gained so much from the hashkafa I learned in sem. Besides, the very fact that you think you don’t need it shows that you actually do, cause every person has room to grow. Now that I am married, I remind myself of the lessons my teachers gave me on marriage and setting up a home and it helps to keep me focused on what my role in my marriage is. These are the kind of lessons you won’t get by staying at home.