Besides ND and polarizing filters, is most creative filtering done in post (ie grading, day-to-night, coloring, etc) or is a wide array of filter types needed for your camera?

You can get the effect of nearly all filters in post.

The effect of a polarizer needs to be in-camera. ND filters and ND gradients need to be in camera (although you can apply ND grads in post if the video does not blow out, although you usually use ND grabs so skies don't blow out).

Filters take no rendering time though, which can be helpful to your workflow. Especially if clients cannot visualize filters.