Upload a video to Youtube without losing contrast
I worked out a satisfactory solution to this problem. It involves adding the 'Computer RGB to Studio RGB' Video FX to each video track in your Vegas Studio project. This effects the rendered file and project quite a lot but appears normal when uploaded to Youtube:
Quicktime

Youtube

It's possible to disable the track Video FX whilst you work on your project so you don't have to deal with dimmed video. The effects will need to be be re-enabled before you render the project.