My tires had around 35,000 miles on them when I decided to over- (or max) inflate them. Not sure how much life I would get out of the tires, but being positive that they were over 50% done, I figured it was worth a try.
I did not notice substantial gains in mpg, although I did notice a bump. (YMMV)
But I did get two blowouts from hitting curbs (one I contacted and one I flat out hit--I figure that one is on me) which has NEVER happened to me before, and I drive/have driven a LOT.
First blowout was around 40k and the second at 45k, so I got 5k and 10k miles of mpg savings, respectively.
But that's just anecdotal evidence, so I made a spreadsheet and did some math.
My general conclusion is, it really comes down to your personal belief:
If you think that better tires (or higher pressures) will get you significantly better mileage, then you should always go for it.
If you think they don't, then you shouldn't.
The problem is, for buying tires, there's not really any way to know what the mpg difference will be, that's why I say it's about belief.
With inflation, obviously you can just try various PSIs to see what your savings is--assuming you are measuring PSI and MPG accurately, and assuming you drive the same way/routes when you measure.
But after all that it comes down to your belief in how much your risk has increased from higher inflation. Whether you believe you have no increased chance of blowout/tire loss, or a much greater one; because we can't measure that.
[I'm now in the greater risk camp. ]
Also currently (as of Jan 2019) gas prices are pretty low, so it's much harder to generate savings. If we go back to $3.00/gallon, these numbers will change.
I used $2.50 when I messed with the sheet.
Feel free to try out the sheet for yourself.
As the directions say, you have to Make A Copy of the sheet in order to manipulate the numbers.
One thing this sheet does not do is calculate tire savings based on differences in tire durability. That extra factor (durability x mpg) increases complexity exponentially, so I omitted it.
But you can assume that if your low-MPG tire will last longer than your low rolling resistance tire, then you need even more mpg savings to justify that purchase.