Much of the discussion seemed to drift away from Panama Jack's original 2 questions, interesting reading in any case. May I have my 2 cents worth?
(1) Variations in Takeoff weight will have some, but negligible effect upon Vmcg. Variations in weight distribution will have a significant effect upon Vmcg, e.g. an aft loaded aircraft will have a higher Vmcg due to reduced rudder moment arm.
Vmcg is evaluated at the flight testing stage for the worst weight / weight distribution. In determining the 'official' Vmcg, nosewheel steering is disabled and is not a factor.
(2) Reduced thrust takeoff should result in a very slight reduction in sector fuel, but you have to be a bit of a nit picker to find it. Optimum Thrust Specific Fuel Consumption (Fuel used per unit of thrust) is generally found fairly close to engine speeds associated with Climb Thrust, anything higher or lower costs more fuel to produce each pound of thrust. TSFC at full takeoff thrust is worse than at Climb Thrust, and the lower end of takeoff thrust derates is usually at or about Climb Thrust.
What minimal fuel savings may occur would be insignificant compared to the massive savings in engine overhaul costs, not to mention the huge increase in safety commensurate with operations well below the engine stress limits.