While not the most diplomatic way to put things, I tend to agree with monkeyBox's sentiment.
A lot of interfaces that I see are terribly compromised by "bling".
When designing an interface for a car one has to think about stuff like
* "how will this be used?"
* "what will the driver be doing when trying to select a playlist, tune a radio station, find a waypoint?"
* "Is the interface easy to discern or understand at a glance?"
If you have access to any materials on developing MFD (multi-function display) interfaces for aircraft, this would be a place to start. They even give simple things like selecting colours for specific uses and screen layout. Intuitionsys, check the library at Carleton. I seem to remember a *****e load of avionics text books there from my university days.
Also, the Apple style guide type documents are a great help as well. I forget the correct name for the docs, but IIRC they go into detail on how to layout information on the screen for low user workload.
When in doubt, think of it this way: will someone unfamiliar with your interface be able to at a glance be able to figure out how to change modes between navigation, tuner, radio, whatever while whipping down a four+ lane highway at 160 km/h? Will they be able to extract information and value from the interface without picking up the fine manual?
Leave the bling for the show and shine Windows weenies that are into stereo competitions. An elegant and infinitely more usable system will get the nod over that any day.
It takes restraint but a month later you'll still like the interface as opposed to thinking it is time for a new theme because the current one is too cheesy.