In fact the UI can be identical for a device with softkeys vs. one with a touchscreen. It causes a few DOH! moments when you are working with some instruments that work one way and some the other, but this isn't nearly as annoying as you might expect.
You still have to look at the screen though. Unless maybe you could 'lock' the UI into one mode (with no sub-menus), which might be a good compromise for vehicles.
The modular scene generally frowns upon systems that need deep menu diving, which is most of the time an indicator that your interface design is lacking.