"If its on its last mission, and its never going to be relaunched, why bother bringing the thing all the way back, just to be decomissioned?"

Heat, power, air, maintainability. Not to mention that the ISS crew rotating out would need a way to get home and the trip is free.

The ISS was built to store/supply all these things for months at a time. The shuttle was never meant to.

Another factor - drag - shouldn't be discounted either. While the drag at ISS altitude is very tiny, it does exist.

Do you have any idea how much it costs to turn around a shuttle for relaunch? Or to build the infrastructure capable of refurbishing and relaunching it?

Of course not. Anyone with even a passing familiarity of the overhaul each shuttle gets when it reaches the OPF knows that only Governments, Microsoft, and Google have the resources to launch a shuttle.

Boeing and Lockheed (A.k.a. USA) might have a passing chance at operating the shuttle privately, but with the vehicle's inherent limitations, dangers, and cost, no one would be crazy enough to lend them the operating capitol, including their parent companies.

Anytime I want to read pie-in-the-sky conjecture about the space program from people who have little to no idea what they're talking about, I come to Slashdot.