The chart on page F-125 of the Mazda 3rg gen Workshop Manual shows that the EGR valve only opens under relatively light loads between 1050 and 3850 rpm. It is closed at idle, deceleration, rpm above 3850, and heavy load. So it seems that there would be little benefit in disabling the system. The emission book, "Understanding Automotive Emissions Control," states that an engine may need it's timing retarded and/or the air/fuel mixture richened to prevent detonation but since the RX-7's valve is closed under wide open throttle we don't need our mixture richened. I've heard from several list members that have disabled the valve with no apparent change in engine operation.