The larger question is what tools would you use on the road? If you broke down would you call roadside assistance or break out the wrenches? That should inform your decision. I generally carry everything (except the jack) to do everything I've ever done to my bike (well, except maybe the specialty tool to do a valve adjustment). Beyond that I'm calling a tow truck (or a friend with a truck). The larger issue again is spare parts, not tires. I had my tool roll when my throttle cable broke, but no spare throttle cable. When my front tire went flat last year, I called the dealership in Missoula (where I happened to be when it went flat). When my drive belt broke in 2005 I was in Missoula again. I had all the tools I needed to replace it except a jack (which the dealer loaned me) and the spare belt (which I got from the Harley dealership). Now that I have a chain again, will I take my chain tool? Probably not.
Now that I have a SPOT GPS Messenger, I'll probably carry even less tools since I can call for help just about anywhere. Things rarely go wrong, but when they do, they're huge (the previously mentioned problems, and the ignitor problems I had this Summer). Every time I've broken down, a truck or trailer was involved, regardless of the tools I carry.
Next year my tool kit might look like this:
Allen wrenches (cuz they're useful for lots of small things)
Screwdriver with some bits
A wrench for the pillion seat bolt
A wrench for the driver seat bolt (these two seat bolts should be allen heads too--I could drop two tools)
A fuse assortment
Leatherman
Cell Phone
GEICO card
GPS beacon
Trailmix and a fizzy drink to tide me over while I wait for rescue
That's about it. I need to buy a slim set of motorcycle-style jumper cables.
