I've taken the first step in cleaning up the cabling for my carputer with the installation of a Pacific Accessory Corporation AAC-NIS2 interface for Nissan/Infinity vehicles. My ride is a 2006 Sentra SE-R Spec V, and despite the fact that this vehicle isn't listed in their list of compatible models, the radio for the factory Rockford-Fosgate system had all the correct buttons, and supported a satellite radio, so I took a chance and it installed just fine.
This interface gives two RCA inputs direct to the rear of the radio, so no more AUX cable plugged into the front of the dash. The sound is a bit cleaner, frequency response seems a bit better, but overall volume is slightly lower; nothing that couldn't be compensated for.
Next step will be to run the cables for the VGA display down through the dash (instead of down the front), then tap some power for that and the new USB hub to replace the passive hub under my seat. Final phase will be to properly route all of the cabling from the trunk under the carpet, and come up with a better way to power the MacBook.