Charlotte is only about 20 - 30 minutes away from the south end of the lake. I would plan some time to visit the city. Lake Norman is really long so it covers a lot of area(it's a damned up river), it does depend on where you are staying.
It does depend on what part of the lake you're on, but anywhere is in close proximity to uptown - if you're interested in museums, restaurants, discovery place, etc.