Why not use the ion engines for station keeping and re-boosting the current orbit? If you put it in geo synch, you can no longer service it, until such time as we build something that can take the servicemen that high.
By 2010 the shuttle will have been in service for 20 yrs and it was originally designed for 15. Its doubtful you could even get to 25; what with some of the 70's technology on-board systems and outer shell/ honeycomb panel structure, batteries, etc that cant be swapped out during repair missions, etc. If we let the last couple years be out of the way of Earth's effects; ie not forced to cycle the Earth every 90 minutes with all the resultant thermal jitter,lost science, etc.. the science retrieval would be great! At least that would be the plan.