So the Tourque gauges on Nav Screen project is going great, the effort is certainly worthwhile.
I just need to get Tasker sorted to automate the device management so the i9000 can be left out of sight in the center console. Touch input may even be possible through the gear stick boot.
So I need to work out exactly what actions I need to be executed and then I can research the method.
Power management: let's assume the i9000 lives in the car, so it's got to sleep or go into power saving mode when the car is turned off... And turn on when the car is started...
So triggers could include power from the 12v USB cable, the BT signal from the Obd plug...
Display: switch on TV Out in Advanced Settings. Since TV out brightness is independent of the device, I9000 screen on minimum brightness and always on (unless ign off), screen locked to horizontal mode.
Apps/Launcher: Initially start the device in Torque dashboard, with the option of developing a car specific launcher later.
The screen res of the stock nav is very basic so unless the i9000 tv out can be downressed it's potential for displaying anything other than medium and large Torque gauges is limited.
Finally I plan to have a go at creating lib specific pids and gauges to match the style of dash cluster.

It's enough for me though just to get corrected speedo, boost, fuelling and temps gauges etc in a very integrated way with minimal visual impact on the cars interior.