Even when I had my 350Z, a lot of forum members warned me about getting work done at a dealership and the fact that you pay through the nose for parts. Although having recently dealt with a dealer to replace a damaged bit of trim on my 370Z, I was pleasantly surprised. The trim piece cost me just over £80.00, which included VAT and the service I received was excellent.
For things like replacing trim or other Nissan specific items, I'm quite happy to use a dealer. As for servicing though, I'm going to stick with my usual mechanic. He's only 10/15 minutes away from where I live and he does provide a courtesy car which is really handy. I've also been using him for 10 years now. So as the saying goes "If it ain't broke, don't fix it".
Parts wise, most changes on my 350Z involved replacing a Nissan Part with an Aftermarket Part, so a Nissan Dealer wasn't really required. Lol. Just as well really, otherwise the Cougar Store and Tarmac Sportz would have lost out on business.