FWIW, I've been having good results using iZotope's RX7 Elements, the Denoise function, for significantly improving the audio quality in Vegas projects. I've found the Adaptive Sampling mode works incredibly well and that two gentle passes work phenomenally well. By gentle pass, I mean to do one pass at 12 dB reduction, save it out, then bring it back in and do another 6-12 dB noise reduction pass. Also, I've found that Adaptive Sampling mode introduces no artifacts at all. It would be great if Vegas partnered with Izotope and brought in the denoiser as a standard plugin to future versions of Vegas.

I remember previous versions of Vegas came with Nectar Elements and I found that to be a fantastic plug-in as well. The attached file shows the original audio file on the left, and the denoised file on the right. You can see that RX Elements did a good job of removing the noise, especially between the rests between the dialogue. There is still noise present, but it went from being distracted to barely noticeable, if noticeable at all.