I never changed the tires on mine and am not sure of how much clearance the wheel wells have.
That engine is very temperature sensitive. A warm air intake will help FE while a cold air intake will lower it.
The 5th gear swap is popular, never did it but a few have had good results.
The SL/SC saturn had very flush windows. Rolling them down is worse for FE than the AC is.
Leave the heater. It doesn't hurt FE but is needed for keeping the windsheild clear for safety reasons.
They can handle an upper grill block as long as the radiator is clean and you don't live in the desert.
For a minor increase, space the headlights forward until they are flush with the hood/bumper.
The rear bumper is a parachute and needs a belly pan.
I miss mine
It was T-boned but its side impact construction saved my wifes life.