If you want to stay in Structures Engineering get an MS (before you forget everything from college and get tied down with a family, etc.)
If you think you ever might want to do consulting, then get a PE license (its not needed if you are going to work for a company; but trust me its a bitch to pass the stupid EIT/PE tests when you are in your 40's and are sick of the corporate nonsense).
If you want to get into management, then a management degree might make sense; depends on who you work for. Talk to your current manager.