I think for city driving, (lots of 0-40 MPH stop and go traffic) weight and drivetrain efficiency play the largest roles since there is lots of acceleration. High speed cruising (50 mph+ without towing anything and on a flat grade) is mostly limited by aerodynamics and your engine's low load fuel consumption. When introducing an incline, weight and drivetrain efficiency start to become more important.
Do you remember how much weight you saved from the new wheels/tires? Car and driver gained between .4 to 2.2 MPG from reducing tire wheel size/weight. See here:
Effects of Upsized Wheels and Tires Tested - Tech Dept. - Car and Driver.
It is unclear in the C&D study whether those gains were the result of a lighter rotating mass or a rotating mass with a smaller radius. They should have tried to test only one new variable at a time.
Then again, C&D tested with a Golf, which is a bit smaller car so a change in tire size may lead to more drastic changes.
10% FE from 8 lbs. of tire PSI is seriously good bit of FE for free. Makes me wonder why auto manufacturers set the pressures so low? Is it a safety or comfort issue?
Roof racks/cages are notorious for decreasing FE. Since about the only thing past 50 MPH past cruising is aerodynamics related, no surprise there.
I wonder if removing mudflaps would make the the vehicle more aerodynamic.
Anyways, good luck with your FE endeavors. I've got a 94 Camry 3.0 and I'm averaging around 22 MPG which I hope to improve.