I'm coming from a bifrost/Maya background, but have seen some incredible examples of grain simulations. I've come to realize that in order to get the look I want the for fine, silty, dry sand, the granule particles need to be tiny. But it seems successfully simming something so small and in such great numbers tends to just slow my scene and machine to a halt. Is there a particular work flow that anyone can show me or direct me to, in achieving something like this?
To set the scene, I basically have a floor covered in about a half inch of sand and need it to fall through a trap door and have some interaction around the edges of the trap door hole. Most of the sand would never move, but I figure having the same consistency and look of the sand all over the floor would help in compositing the sand over the existing plate.

I think you should try using Vellum for such an effect.

Check these tutorials out:

https://www.youtube.com/watch?v=hQN5pUrYjKQ [www.youtube.com]
https://www.youtube.com/watch?v=AGPug-p_M2s [www.youtube.com]
https://www.youtube.com/watch?v=lAor5pTZyvw [www.youtube.com]