Well, I reckon I'm living proof that fuel price increases get people thinking about economy mods; see this thread:
https://www.turbodieselregister.com/forums/showthread.php?t=124030
It seems to be the consensus around here that many performance mods actually improve fuel economy... but, of course, only if you keep your foot out of it. Its pretty easy to see how things like a FASS, or a moderate injector upgrade, or a good torque converter, could increase the efficiency with which fuel is converted to 'go'... and so, of course, if you don't use that extra 'go' very much, what you get instead is increased MPG. Then there's another class of mods (propane injection, for instance) which, in my mind at least, are open to question (they increase power but probably don't increase fuel economy). Finally, there's all the 'kid stuff' (no offense, kids... I was one once, too, but you get over it) -- extreme fuel plates, monster injectors, lifting, big tires -- that are obvious mileage killers.
I think more and more of us will be interested in MPG mods. And hey, if nothing else, its a great way to convince the little woman that all those BOMBs aren't a complete waste of money!