The flame kernel is what is changed with the quad tipped plugs. This
increases the efficiency of the engine, increasing power because more of the
gas/air mixture is burned.  Thus less pedal is required to maintain the
desired speed and mileage increases because less raw gas is wasted. ( But
also with the increase in power, more pedal is used because of the increase
in power...)

Changing the plugs alone will only give a small increase in power, this is
also dependent on the condition of the rest of the engine and related
systems.

My engine starts with just the slightest bump of the starter.  I have also
modified and changed several engine parts and made changes to the supporting
systems to increase the power and make use of the plugs...

Robert