Personally I did the maternity21 test which is far more accurate and a simple harmless blood test. I feel like I can relax after finding out al came back negative (I am also a NICU nurse so I see the atypical baby every day). I feel like I needed this just for peace of mind. Typically insurance covers it, and if not it's a max of $200. It also tells the gender as early as nine weeks if you wish!
We got the NT scan for our last pregnancy and we did get a false positive screen and it did cause undue stress. But to be honest I could not wait for week 20 for the routine ultrasound. I wanted the earlier NT scan so I could see a heartbeat and know things were progressing smoothly. So it had both pros and cons for us. You are still young at 30 and I believe it is recommended for 35+.
Unless your looking to prepare in some way or abort I would say it won't hurt to skip it. I know that worry is there but with the uncertainty in results that added stress won't help. My husband and I have opted to skip this test and only do tests that will change our pregnancy care or delivery options.