The ESA recently announced plans to develop a station halfway to the moon. This station would, I presume, serve as the next international station replacing the ISS. While I understand that the ISS is aging and some modules are at the end of a useful life (see this question), there are still sections that have lots of life left such as newer modules and the truss assembly. What are the obstacles to keeping these sections by pushing them to higher orbits and utilizing them in a new larger station. Considering the cost of getting anything up there it would seem appropriate to re-use whatever we can. So what are the obstacles in reusing portions of the station?
A corollary question: What parts/sections of the ISS would be salvagable?