Have you done any modifications so far? If you're monitoring temperatures and in regular driving, grille blocks should be in line, and can be tasteful.
I saw you mentioned the exhaust, but an underbody would be a great point to expand on. mcsrews was successful with his Q45 build, and my polycarbonate hasn't had an issue yet.
Rear wheel covers could be in line, but definitely more noticeable. Have you went through
65+ Vehicle modifications for better fuel economy - EcoModder.com for ideas while you start working on what you like from
100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com
It will be a little while before aero mods will be more so beneficial than driving technique, but the DC commute will help. I found my FE wasn't so bad at higher speeds in the traffic, but I imagined it because we were such a cluster moving through the air.