Are you doing stills or animation ? In my experience stills are not the problem with xstream. But animation is. Rendertimes are terribly long to get trees to stop flickering, even without any fancy skies or vols. I can use particle flow and multisub mats and maps to place thousands of random (scale/rotation/material) proxy trees around the scene in just a few minutes, and even with transparent/translucent leaves, rendertimes for 1280x720 animations are around 20 minutes/frame with MR. Also, I do not like the way that the Vue trees look when up close to the camera. They just dont hold up. They do look alright from a far distance, but not up close. Especially compared to EM or Onyx trees. And with Onyx you get wind animation.
IMHO, if you are going to do heavy Veg “animations” in Max, you are better off just using proxy trees/bushes/flowers instead. They will look better and render ALOT faster. I dont just say this from reading forums. We have had Vue xstream since version 6, and have only been able to use it successfully on 1 project. And this was mostly because we had no real deadline.
Here is a frame from a first draft animation that I am currecntly working on. It isnt that great, I know, but the trees are animated, and the rendertimes without flicker are about 20 minutes/frame. The Veg in this file is still just instanced, not proxy, and there will be about 10 times as much as there is now when the finals are run. And there is no variation applied to the materials yet.

This image is not going to wow anyone, its just to give an example of what is very easily done in Max without Vue for animation.
Let me say lastly, that the only real way to find out for sure if Vue is going to be good for your particular pipeline, be it stills or animation, is try the demo for a while. I always take into account what others have to say about software, but I always try for myself to be sure.
Regards,
Mike
BTW, nice pod racer you got there Evan. It looks really cool.