Don't forget about the RenderScale setting. What I used for nerfing the followers while maxing out the main was:

Follower:
/console renderscale 0.3

Lead:
/console renderscale 1

This makes the terrain/buildings/chars look like minecraft on the followers but the UI elements don't change.

[EDIT] Just be aware that this may induce a half-second to 1 second delay when swapping leads as the WoW engine catches up.