I replaced bald tires with a set of 2 year old hardened stock tires from a diesel pick up and I got worse braking traction. Also had other experiences with using older tires. I test drove a Mitsubishi eclipse with dry rotted back tires that made it want to slide out on turns. Usably the old tires had little visible cracks too.
85 Chevrolet. 30 MPG or bust!
One thing with new tires is the diameter is larger due to tread not worn away.
So actual distance covered per rotation is more - but your speedometer doesn't know this.
The difference vs. a half-worn tire isn't that much - but vs. a worn-away tire the difference is more. If you make speedometer stay at same speed you used to (with worn tires) the engine is actually working harder because it's driving the car faster. But the odometer shows slightly less miles.
If you stay off the gas a bit you likely will get better ACTUAL mpg but it won't show on the odometer. Like having a slightly taller final gear ratio.
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.