$9K for 9K miles is slightly under Kelly Blue Book's suggested retail of $9585 for the Chicago area. Given the mileage, and assuming the bike is, overall, in a condition appropriate for low miles, this is probably a decent price. Check the tire wear. Agreed that, if these are the original tires that came withe bike in '04, they should be replaced sooner than later. OTOH, at 9K, it's fairly likely these aren't the original tires - end of problem, one hopes. Brake wear... who knows, maybe the PO was hard on the brakes or let them drag a lot. I'd at least ask the dealer for any service history on the bike.
Check the seals in the drive shaft for obvious signs of oil spray or weeping. An oily film on the back of the housing for the drive shaft is Not A Good Sign. The problem can be corrected. I'd let the seller either pay to have it put right or take a hit on the price, equal to the cost of the repair.
Past that, there are the usual used bike issues (how's the battery - 7 years is just about the end of the road for a battery). There are smaller issues that should be looked into - for example, the quick disconnect fittings in the fuel lines at the fuel tank. BMW's original plastic fittings snap off sooner or later. When it happens, you won't be happy. Either the PO replaced the plastic bits with metal bits or you should do it (~$80 in parts).
Commuting on the KGT... sure, you can do it. You won't be maneuvering like a little Vespa, but the bike handles well enough in stop and go traffic. Remember, too, the bike is water cooled, so that when the weather's hot, and you're stuck in traffic, you don't have to worry about the engine cooking itself, as it would if it were air cooled. Two things I'd add to the bike, particularly for city and commuter riding: a plastic headlight protector from Cee Baily (1/8" polycarbonate shield that will stop rocks from trashing the headlight - $500+ for a replacement), and an oil cooler screen (try the one from Wunderlich), also to minimize thrown rock/debris damage.
Good luck with your KGT!