What an interesting concept! Mixing an inert gas (exhaust gases) with your fresh intake charge to increase fuel efficiency! And more is better?!! Say, why not just run your engine on argon or dry ice??!!
Why do you guys think the factory cuts off the EGR during WOT, when you need the most power out of the air-fuel charge for passing, merging, etc., ??
Why do you think racers of every kind do everything they can to PREVENT exhaust gas dilution of the fresh intake cycle, and have been doing this for maybe ninety years? Why do you think the fire department has inert gases like CO2 in their fire EXTINGUISHERS? But you are going to show us how to get more power and fuel efficiency from a gallon of gasoline by COOLING the fire in your heat-engine. Well, when you figure it out, there are a bunch of multi-million dollar NASCAR teams that will pay you very well for your discovery.
EGR is for emissions. Period. If the car makers had not been ordered to find ways to reduce photochemical smog (which they decided to do by cooling the burn), there would be no EGR systems on our engines. If the carmakers had been ordered to prioritize the increase the fuel efficiency of cars above everything else including emissions, there would be no EGR systems.
Yes, if you block off the EGR passages (or if the valve plugs with carbon), your engine very likely will run worse. This is NOT because EGR makes an engine run better, but because when EGR is added to an engine, the ignition curve and fuel system calibration are altered to work with the EGR. Basically, because the air/fuel charge is polluted with exhaust gases it burns cooler and slower, therefore the ignition has to be advanced to start the fire sooner. If you blank off the EGR (which is what other folks would do to get more fuel efficiency or power or some combination of the two) you are left with an excessively-advanced ignition, yes, the engine certainly will run worse (until you re-curve for the new conditions).