Sorry to hear about the accident, nice to see another NISMO, and thanks for your service. There's not really much big upgrades you "need" to do if your not going for more speed/power. Besides what was already mentioned.
1. Audio. Anything is better then what comes from the dealer. Check out the Audio section
2. Lighting. Lots of things you can do with the headlights, ONEighty has some nice things to think about. LED lights for the interior and rear license plate to replace the yellowish non led lights. Oh and the GT-R start button =P.
3. Clutch helper spring change to help the feel of the clutch if you have the manual. Hood struts the replace the cheap looking rod that holds the hood up.
4. Exterior. I personally like the Zspeed under shroud, much better then that plastic crap under the car. Finally not sure about your state rules for front license plates but a retractable holder would be nice, but there are many good options out there w/o the dealer drilling holes in your bumper.
5. Oh and change out the seats and sell them to me.
JK, I wish I had the seats that come with the new Nismo Zs and Jukes. No need to ever change those.
There are many little improvements that you can do and I am sure in time you'll see them all mentioned here.