Recent few queries sort of inspired me to clarify this…. changing the look and feel will not change the User Experience. User Experience is not just one thing, its a combination of good workflow, architecture which includes information hierarchy, usability and graphic design. Please note graphic design is one of the elements and not the element. What is UI then? User Interface is a set of controls that you give the user to operate the application/software/product. It is a layer on top of the architecture of the product. These controls can be arrived at, after the designer has decided what would be the different screens and how would they be linked together. UI changes may or may not affect the architecture.
Graphic Design enhances the look and feel of these UI elements. So one without the other cannot change the User Experience of the product.
Workflows are most critical in enhancing the user experience. Series of steps to achieve a task defines a workflow. A good UI links these workflows together seamlessly.
So if you looking for a change in User experience, you should be prepared to relook at everything that forms a part of the product.