You just need to look at the trader section on NS to see that the market is cutthroat. And it's not just ppl who are importing brand name parts locally.
I mean look at what Just Jap are doing now. It basically sounds like you're trying to do what they are, about a year too late.
I agree with Richard, find a small market and tap into that. I wouldn't call catering for Skylines, Silvias and rotaries a 'niche' market