My 2¢ on the space shuttles

I know I'm a little late on this, but over the past weeks there has been talk of NASA's new budget.
A part of that new budget is the long in the making retirement of the space shuttles. And really, that's a good thing. They are starting to be unsafe and hard to maintain.
What I question is that they are being mothballed.
Now I'm not sure that this will completely work, but is there a serious reason why we don't launch them one last time and just leave them docked to the ISS?

Of course in my mind the ISS connects together like a K'NEX or LEGO set, so I don't see much problem with each shuttle carrying a connector to attach to yet another shuttle to the station. It would greatly increase the work space on the ISS, and since they aren't coming down ever again we can even put solar cells on the underside of each shuttle to supply more power.