Nick,

“of course, right now there is no clearly-defined law in space, but my assumption that general international marine law should apply is a reasonable one”

That is a common misconception by people who have never taken a course in space law. But if you have you would understand that the context of the OST and subsequent space treaties was that space was not the high seas.

Nation states, or their agents (i.e. Private firms) retain ownership of objects in space even when they no longer function. To take them deliberately would be regarded as theft. The concept of maritime salvage simply does not apply to space in any form. Sorry, but that just how it is.

As noted on the UN Space Law FAQ

http://www.unoosa.org/oosa/en/FAQ/splawfaq.html#Q9

“Who owns satellites and other space objects that inadvertently return to earth or become "lost" in outer space ? Can they be claimed by anybody able to salvage them ?

The Outer Space Treaty states that ownership of objects launched into outer space, including objects landed or constructed on a celestial body, and of their component parts, is not affected by their presence in outer space or on a celestial body or by their return to earth. In other words, satellites and other space objects remain the property of their original owners regardless of their location. The Outer Space Treaty and the Rescue Agreement then go on to specifically provide for the return of all space objects or their component parts to their original launching authority or state of registry if they are discovered or recovered in a foreign territory or on the high seas.”

Try picking up relicts form Apollo 11 and returning them to Earth and see what happens. You won’t be paid for recovery, you would be charged with theft of federal property. And if you find U.S. space debris on Earth, even on the high seas, you must turn it over to the U.S. Government.