Heres what I did back in the day...
Im not sure how much it helped mpg because that was in like November and winter came right away... It DID help the car heat up quicker in the winter, something festivas dont do very well.
And of course it got looks...
Its stock now, well except for the engine of course... but if I do anything it would be a more "normal" lip spoiler and a belly pan... I like the car as a sleeper and dont want it attracting any real looks unless I hit the gas.