I'm still using v3. I tried out the demo of V4, and couldn't find a compelling reason to upgrade, especially when I now have to buy-upgrade differently than before. One of Maxwell's strengths was not only its quality and Pylon's integration, but all the plugins came with the purchase. Now I have to choose, and my rendering doesn't benefit from the GPU improvements that much in the benchmark test I ran, but I am running older Mac systems.
I think if Renderzone had improvements such as a rendering engine improvement, that would be awesome. I also find myself disappointed with FormZ's material libraries and material creation tools. They really haven't progressed since v6, and with the new v8 GUI, there are many bugs an less than intuitive changes.
The last thing that has changed in my workflow in the past two years is the inability to rely on the Imager, which was my assistant for many years. I would set a batch of views and let that render on another machine while continuing work on another facet of a project. Today, the imager remains a broken piece of software, and while I've spoken with Tech support a number of times, it still does not do what it did in v6. Simply allowing one to save an imager file with the parameters you want for a batch of images, setting it working and then getting those results without render engine problems or the software settings defaulting to wireframe, etc.
One of the great things about Maxwell is the multilight setup. One of the most difficult things for me to work with is the multilight setup. : ) It would have been nice for NextLimit to offer just a very light upgrade price for one plugin...but until the move it a bit further and Pylon has a chance to update the plugin, I'm gonna stay at v3.
Again, much appreciation to Pylon. Their support, like the formZ tech support is fantastic.