for daily driving and feel the motor mounts and short shifter are the best. if i could only keep one mod on my car i would keep my short shifter.
for getting more hp or torque, get yourself a test pipe or cobb sri... test pipe is 100 bucks and i think the cobb is around 160. install on a test pipe is simple, so is the sri if they have the new brackets and you don't have to fab your own.
FMIC is big bucks (a grand), but you could fab your own for around 500 if you wanted. I will not argue that they are performance monsters, though. i envy everyone who has one on this car. you get free boost from less pressure drop and cooler air into the engine...