Robb, don't get hung up on wanting a low mileage on. The ST1100 is built like a brick outhouse and if it's been looked after should be good for 250,000 km or so. So, the order of importance I think is:
Maintenance history: Remember that ST1100s haven't been maintained by the Po-Po for maybe 8 years or more so you want the previous owners maintenance records too
Condition: What do the fairings, tires, etc look like, what does the engine and gearbox feel like.
Mileage: OK, it'd be nice to get a low mileage one but don't worry about looking at bikes with well over 100,000 km if you're happy with maintenance and condition.
One thing, Po-Po bikes, even up to 2002/3 models (and I think you'll find the VIN for 2002/3 registered bikes is for 2000 manufacture) continued top have the larger grey engine cover where the civvie versions had a smaller engine cover from about 1996 - I've got a smaller engine cover which doesn't fit my ex-Po-Po bike. Thinks to himself, must list this on OzSTOC!