The “motion blur” implementation, as far as I see, is very inefficient because it renders several frames each time, such that it renders the same frame repeatedly instead of keeping it.
Nevertheless, I think that “blur is like Brylcreem: ‘a little dab’ll do ya.’” :yes:
Simple vector blur, taking the vector (say) from the head, will produce a very believable result and can be done “in post.” All that you really need, to carry the effect of smooth motion, is blur of some kind.
Another trick that I have used is to superimpose a non-blurred track of an object, at 75% opacity, upon a blurred track at 25%. The numbers, of course, total-up to 100% when the two channels are combined with an Add node. The outcome is a mixture of blur and sharpness, done “computationally on-the-cheap” in the compositing stage.
And … if someone’s mind is set on “luscious, individually-bouncy hair,” use a little more of that Brylcreem. The hair doesn’t have to bounce; it doesn’t even have to consist of particle strands. Give your star a nice hairdo that doesn’t bounce all over the place. Maybe drop some particle-hair action on a few extreme-close-up shots early on, to set the viewer’s expectations, then use a simpler strategy in most of the shots that are taken at any distance. You might notice the difference, but if your production and your story are compelling, the audience won’t care.