I think it would be a good idea to have boost gauges in the interior of cars, i think it would make the game feel more realistic instead of having a boost gauge only in the HUD
IIRC some cars have factory boost gauges (I think the high end I-Series do). Aftermarket tachs and boost gauges would be nice to see.
We need more customization in the cars interiors. Period. The bucket seats and shift lights are nice but more can be done.