There's a thread going on elsewhere in the board (I think in the Lounge) where a guy with a White T-Type is doing the same thing. His setup sounds really cool, but its in the works so no pics yet.
I had it in my head to do the same to my GN, but the one I ended up buying is really low mileage with a perfect interior, and I dont think I'll have the heart to hack it up. I'm gonna wait for the next car to do it, but this is what I had planned...
Black suede or alcantara headliner
Black dash and all panels
Reupholster seats like this: Where there is black fabric, replace with high-quality black leather; where there is gray, replace with black suede inserts with diamond stitching
Aftermarket steering wheel in black leather
GNX-style gauge cluster with all deep amber/red lighting
Possibly contrasting stitching to give some dimension
I'm not crazy about the light gray tone or the seat fabric used in the stock GN's, so if I were to redo it I would just go all black - it looks a lot more sinister and would suit the car better in my opinion. Might be too much black for some, but thats what I like