I hate to pile on to what this is probably going to become, but I wouldn’t go hard on mods. Especially if it’s a manual, a simple car like the 2 is becoming very rare. Major mods will either be crazy expensive and disappointing or cheap and disastrous.
I believe there are some suspension mods that will bring the top-heavy feeling down. That and better wheels and tires will make the car feel more sporty without tearing into the powertrain.
I’m spouting from very old memories here so please google this and verify, but I think Mazda set the range/empty warnings to be extremely conservative because the fuel pump is submerged in the fuel tank and running the absolute full range can cause the pump temp to increase at the very bottom of the tank capacity.
So the useful capacity is less than the actual specification for a full tank. There may be some reduction in fuel efficiency because of the auto being a 4 speed and you driving in a hilly area, but the range being less than expected was a common complaint when the car was new.
Owners would test this by running until the fuel light came on and then filling until the auto shutoff hit the first time (don’t fill into the fuel neck). Whatever that amount of fuel is, is the capacity you should divide by to determine MPG. Back in the day this math, dividing miles driven by actual fuel consumed, returned a fuel efficiency within the expected range.
Some owners then made a habit of driving every tank “past empty” because they knew the warnings were conservative.