Since my last graph I have gone a few more km, upped the tire pressure from 32 to 40, replaced the two rear tires to match the fronts, replaced the doughnut with a full sized spare + added bunch of other gear (probably net change +60 lbs)
Blue is before (99 points, 1543 km total)
Red is after (81 points, 1884 km total)
In a way it is too bad I did so many changes at one time so it's hard to say what had what affect but the car handles a bit better now and I have much better piece of mind driving in remote areas while any change in milage appears to be a wash.
Oh and I did some more controlled tests on AC on -vs- AC off and it appears to affect my consumption by about 0.2 L/100km @ 100km/h. At $1.40/L I will gladly pay the 14¢/hour it takes to keep me cool and comfortable with the AC on in the summer.
EDIT: does anyone know why my my graph is so small?
2nd EDIT: Thanks Metro