according tot wikipedia your version has a bodykit that lowered drag over stock... i think the Cd for that car was 0.28 but i could be mistaken. and some winder tires and a bigger engine with slightly less grillblock could send you back a little...all in all the aerodynamics of most details are pretty well sorted. so i'd be carefull with to extreme mods.
what you could do is a grill block, i'd keep it simple, see how hard it is to get the grill unbolted and put something behind it, make a vertical slot in it if more cooling is needed... keep in mind that something you could get away with in winter might not work in summer, but if you make it so it can be pulled out quickly no need for fancy mechanisms. (always cool if it does work, but sometimes simple less perfect things get actually done while perfection remains a dream)
next i'd recomend an undertray if there isn't one. try covering the area before the front tires and perhaps between then over the engine bay... the underside should be realatively smooth . than i'd do tire dams, front and rear wheels. (if you make them light you can glue them onto metal bits with construction glue, no drilling required) look at oem setups and don't make them to big dams that are to small will still reduce drag, dams that are to big will add drag
warm air intake is a real good thing... if you have a cold/warm air intake valve in the airbox you can make an incert that prevents the wai from closing fully... you'll get warm air all the time.. you'll se FE go up and power go down! it's a trade of but you have a big engine so the car should remain more than drivable with a few horses left!, plus a good drivestyle will make up for them. i'm flirting with 40 since i have it but i think the post holliday traffic and winter well put an end to me FE rise... i will keep an eye on how the wai affects my winter milage wich is traditionally bad.