Even though the 42k miles is really low, I don't think $21000 is a great deal. Probably not a total rip off, but, not a steal anyways.
The 2001+ have some nicer features that I would GLADLY give up the extra 20,000-30,000 miles to have. ie. nicer tail-lights, and NAV with DVD instead of the hard-drive setup on older models, the minor steering improvement,
In August 03, I paid 23,995 for a silver, very clean, 82,000 mile GS400 with NAV, htd seats, 17" chrome, CD, etc.