Well the Mac Mini would be more powerful. You could hook up a dash cam and record video, and you could use more devices to control it, and it wouldn't skip, it would be quicker, etc...
That isn't exactly the point of the project...
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This is a good screen: http://www.amazon.com/dp/B000AYG9F6/ref=nosim?tag=spajr-20&linkCode=sb1&camp=212353&creative=380549
Or this one: http://www.google.com/products?q=Xenarc+705TSV&hl=en&aq=f
If you got a new Mac...