NOS needs a rather healthy mixture to begin with (As I recall it helps
with cooling)...

NOS adds a bunch of heat to the engine, so no, it doesn't help with cooling.
Basically, it's a safer way to add oxygen to the incoming air than injecting
oxygen directly... so since the incoming air is now much more oxygen rich,
you need a bunch more fuel, or your mixture will go very lean. In that
sense, it's an alternative to turbocharging... but the NOS bottle will last
a minute or so, OK for one takeoff... then what? :-)

Paul, turbo Cardinal mode