What is the best way to refinish a worn pine plank floor?

In my opinion, plank pine floors look best weathered and aged, but clean.  I would recommend just removing the worn finish with steel wool and a solvent and brightening up the floor with a new coat of polyurethane.  If you are looking for a like new appearance you will have to sand but I might recommend a pro since the pine floors can be so soft you can sand more than you should very easily.  And since pine, as previously stated, is a soft wood, know that you'll soon have a new set of marks and scrapes.