The new dampers did the trick. Not a peep out of the belt anymore!

I probably wasn't hurting anything with the worn dampers, because the belt was showing no sign of wear, but it sure is nice not to have to listen to that squeak.
Looking at the PO's records, which he was nice enough to provide me with, I noticed he took the bike in to adjust the belt at 13,800 mi, and then again at 14,200. I suspect he noticed the squeak and took it in the first time, they didn't fix it, he took it again shortly later, they still didn't get it so he gave up. Dealer probably told him they all do that.
How long should brake pads last? He has had new front pads put on 3 times in 16,800 miles, and the rear pads done once.
Also, I was able to adjust the rear wheel so belt tracked in center of pulley, and it stayed there while I turned the wheel either direction by hand with bike up on block. Didn't look at at it while underway. At this setting, the position indicators ( by the adjusting nut ) are within about 1/4 mark of each other.
I set the tension with the tool, and tried the 90 degree method and ended up just about the same, So no need to invest in the tool, but it makes it a little easier to set the tension. Just stick the gauge in and turn adjusting nut till gauge is at the middle line.