Canon 7D user thinking of switching to Nikon D600, big mistake?

"I know that lenses are more important that bodies"

And creative seeing is more important than both together. I realize this will be an unpopular reply on a gear focused forum but no camera, no lens ever made a great portrait. The problem you are experiencing has nothing to do with your gear. Award winning portraits can be achieved with the equipment you have. Your lens hasn't become stale, you have. Sometimes a new lens can help shake out the cob webs, sometimes not. If money is tight, try other approaches to portraits that you may have not tried before. Hard light instead of soft. Wide angle instead of long. Different locations, points of view etc. Look at some good portrait work for inspiration. The answer to better photography is within you.