Shouldn't be a problem using vertex color. How does the example scene look?

You shouldn't get this issue though, strange.

If you open the example scene in SF, do you get the same issue on the plant there?

The dithering is probably due to the shadow bias settings in your directional light.

Are you sure both the camera and the project is set to forward?

SF doesn't support deferred yet, you need to use forward for your vertex animated / transparent shadow casters

Are you on deferred or forward rendering?

I've considered async node refreshing as well, though it would require some restructuring at the moment. That said, it's still a problem in calculation speed, it can be done faster. The node previews are currently done on a CPU level, while it could/should be done on the GPU

There's now a checkbox in 0.23 for disabling node-preview updating, zoom is already open in another topic!

A Normal Blend node is now implemented in Beta 0.23 :)

(Though it's only with the reoriented normal map method, simply because it's yield the highest quality for a very small cost. If you want the other ones as well, request it in a new topic!)