I did some research on this a while ago before binning the idea and going for the stand alone Sat Nav. If your system is running 5.0 or 5.1 you can not get any upgrades for it. Basically Nissan fitted the system into some of the 2004 models but not all. Some were fitted with a newer system running the 6.0. Because of this they never made a updated version for the earlier system. Therfore if you do have a disc that has the 5.0 or the 5.1 forget it they dont exist. Now if i'm wrong and you do find a way to ugrade the existing system dont keep it to yourself. Good Luck.
It's far too much work to be completed by hand. you will never get the same finish as with a DA. If you want to drop by some time i'll give it a go with the polisher. drop me a PM.