Re: How many Shuttles could have been kept operative..
That would not suffice.
It is funny how short people memory is. Shuttle with the flight profile restrictions used for the last missions after the re-entry disaster would not make it to Hubble orbit and back. This was part of the "safe" profile discussions after the accident.
So frankly, we are back to the drawing board in any case and the need for a proper orbital tug. Something which is long overdue.