I love World Creator, especially the vegetation distribution pipeline. You can create some very realistic fields with it. Im going to check out impostors too - ive seen it a few times and wondered what it's about.
Stupid Rental. My Zbrush that I haven't paid for an update in years and is perpetual Trumps that on all counts.
3D artist Bryce Szandro released his hard surface kitbash set featuring 20 pieces that can be reused in many ways. The pack includes original Max and Zbrush files for you to edit the models.
You are free to use this kitbash set and modify it how you wish for personal and professional use.
You can also email the author if you have any questions or suggestions.