I would suggest use layer comps, so one PSD could have many mockups for the same website, and updating the content or appearance of one layer would be a breeze.
If you can’t do this you aways can put in version control (but will be heavy).
ONE LAST THING On photoshop you have a resource called SmartObject, so you may have a PSD only for the footer, and by changing this PSD all you have to do is update the smart object on Photoshop. (SmartObjects can be used to place PNGs, GIFs and other image files inside Photoshop allowing to modularize your PSD Files (DRY Photoshop =) )).
This is the best solution… +1