Yah ive had my 33 now in NSW for 6 years since moving it back from adelaide. Rego is now NSW. The only drama you will have is that if you have a NSW license you will need to have it registered in your name in NSW plates. Unless you can find a mate in SA who is willing to have the rego at his/her address. And i know what you mean about cheap rego. When i brought my ## down there it was like $400 bucks and that included rego plus green slip.
On a second note. In the 6 years ive been back home in NSW my 33 has been pulled over numerous times but only for a 'Random Breath test" Shes lowered, 3 inch exhaust, hi flow turbo, FMIC and lots of guages. But the cops never have once asked to pop the hood. Might be the fact i dont drive like a dickhead. But yah you might have trouble getting a blue slip for your new rego as your car is ment to be back to factory specs when inspected. Try find a place that will blue slip a lot of imports. i.e ask JEM, Top secret im[ports blacktwown, Unique autosports seven hills. Ect ect.
Good luck