I was under the impression from reading something in the Vegas Video forum long ago that changing settings on the advanced tab only altered the quality of what's shown in the preview window, not the actual created file. Am I remembering incorrectly?
Nope. Preview window quality setting adjust the preview. Render panel advanced area affects the render. If you find yourself using more than the stock DV template, set up your own.
BTW, preview quality on final renders looks the same as good on 95% of what Vegas can do. It is much faster, more like other NLE apps. speed wise. Deform filter will show some loss, and there is no frame resampling in preview quality.
SF said they would give us the lowdown on what goes on behind the scenes with the different settings.