Welcome to EcoModder!
I think the Contours are very sleek looking cars right from the OEM, and there are plenty of mods that would easily complement the styling of the car while making it more aerodynamically efficient.
If it's mostly highway, the next time you change your tires, go with something that has a high sidewall pressure, like 44 or 51 PSI, and keep them there. You won't notice too much, because on the highway, ride isn't always so important.
Rear wheel skirts, followed up with the OEM aero kit from the SVT Contour will help out a good bit, and give you a great starting point for even better aero mods later on, as you have the time. For instance, the side skirts from that kit have lips on the insides that make a nice mount point for a belly pan with full side to side coverage.
A full grille block can be made to look like it's not there by using some thin plastic, like that used in blister packaging (Remember that when you buy your kids toys.)
If you're concerned about the look of wheel covers, you can check out MetroMPG's smoothies - they look like the OEM hubcaps on his Firefly, and IMO, they're pretty damned nice.
I wouldn't worry too awful much about the wipers, since they're probably locked in a bubble.
Insulate your exhaust manifold and piping/cat. This will aide with scavenging, reducing pumping losses in your engine, making it more efficient at sucking in air, which is what it has to do to create movement. This will also allow you to run a full belly pan with less worry about whether or not you'll melt Coroplast or overheat aluminum paneling.
It would be in your best interests to check out
65+ Efficiency Mods and
100+ Hypermiling Tips for more information on aero modding and eco-driving.