I know underhood temps willl be similar but it hits well over 100 degrees here for 3-4 months out of the year and my car is driven daily no matter what. I would hate to go through all the trouble and not even notice a difference
if your car is running fine as is, then keep it.
i changed mine out for two reasons: (1) because i needed a new coil pack anyway, and, at the time, the 1.8 set-up was about half the cost. now, the 1.8 coils cost twice as much as the 2.0 coils. i would have to think twice about it now. (2) mazda was running the 1.8 set-up on the world challenge protege race cars. if the set-up was good enough for them, it certainly should have been good enough for my car.
check out that engine bay (crazy)