Chasing after the whole "why does my render look different from the preview, I found this among one of the very helpful posts:
Install SeMW Extensions. Enable its Preview levels extension (Tools menu > Extensions), which will put a new dropdown menu above the Vegas preview window. In that dropdown menu choose "PC". You can safely render with that set, as it applies to preview only.
THIS IS NOT TRUE. Don't get me wrong - the extension works great (I had to adjust the gamma a bit to match on my system) and it takes much of the guessing out of the render game, but IT DOES AFFECT THE RENDER. It adds the Levels plugin to the Video Bus and needs to be turned off - just like the instructions for manually setting up the levels. You can use the drop down to go back to "Original," but I prefer to do it manually, as the dropdown, in certain circumstances, will actually add a second instance of the plugin to the Output FX/Video Bus chain.
Again - great extension. Needs to be turned off before rendering. (Unless I'm missing something - and if I am, please correct me, as I would love to not have to remember to turn it off...)