I have very similar tastes to yours; I like painting on a black background. It looks great. And although I haven't tried any paints other than acrylics recently, I vaguely remember when I used to paint with watercolors, and the feeling is not even remotely the same. Each material is a universe that, through trial and error, you could specialize in. Of the ones I've tried, I would always stick with canvas. Heavyweight paper has its own timing and characteristics, and I feel that when you use more than two layers, the magic is lost. This is not the case with canvas, which allows for many layers and textures. Regular cardstock has a different timing; I've tried some that are impossible for me to paint on.
Canvas, as you say, also has the ability to be reused, which is great.