My power and MPG went up slightly when I swapped in a 180* T-stat for the stock 197* in my '00 Ranger, and my engine, belts, hoses, and sensors should last longer because they're running cooler.
The 3.0 engine is an old design that wasn't originally meant to run at such a high temperature, and I strongly suspect that the high temperatures are at least somewhat responsible for the spate of head cracking that we hear about on the boards, and also for the cam sync problems (the heat thins out the oil which lessons it's lubrication properties in an area that is already marginal).
Ford no doubt increased the 3.0's engine operating temperature in later model Rangers in response to tightening emissions standards, but my Ranger has had no problem passing emissions with a 180* 'stat, so there's really no reason to run anything hotter.
Power will go up but MPG will go down, they are on opposite sides of the same coin.
Lower operating temp causes a richer fuel mix, that's an old CAI(cold air intake) sellers trick.
CAI really doesn't do anything but the lower temp t-stat, they recommend, does, lol.
This is why an engine seems to have more power in the winter, colder air, but also why MPG is lower in the winter, colder air.
Outside of overheating, sensor life/operation wouldn't be hurt or helped by the 15 deg difference, same with the oil viscosity.
The cracked heads are from repeated heating and cooling cycles and a weak point in the original casting, a high temp overheat expands the metal even more so the weak point will often crack at that time regardless of age.
I think it was Ford that pioneered the high temp t-stat, around 1965 was when some ford engines were first equipped with 192deg t-stats.
The reasoning was from long term tests they and SAE had been doing, it seems that with a 200deg minimum operating temp the fuel and water in the oil will be dissipated faster, their testing indicated about a 30% increase in engine life with the higher minimum operating temp.
I think the 30% is a bit optimistic, SAE tests do show much higher engine wear when operating temp is below 140deg, above this the decrease in wear gets less and and less, so 192-197deg t-stat would produce less wear on oil lubed parts than a 160 or 180deg, I don't think it would be 30% better.
Ford also started recommending 6,000 mile oil change schedule around this time, for engines equipped with 190+ t-stats, because oil would stay cleaner longer.
Anyway that's the reason for the 190+deg t-stats they use now, less engine wear, and added benefit was better fuel economy.
As far as emission, I don't think it would matter too much, but burning less fuel per mile on it's face would seem to lower emissions, but never looked at that specifically.
But you will get more power with a 160 or 180 t-stat, for sure, ask any racer.