The reason there are different answers is because people do things differently and scenes vary too. The best way to figure out how much room you have is to experiment.

The contrast of all film's can be adjusted in development. With color work this can significantly change the color balance/rendering. That said part of the magic of Velvia is the strong contrast.

One alternative for contrast control is viewing Velvia, Provia, and Astia simply as contrast control choices.

The other thing you might experiment with is color filters and polarization. Warming and cooling filters can make any of these films more or less vibrant.