Hi Paul,
Thanks for your comments and observations.
My primary reason for replying is to let everyone know that the Planetside staff is very much aware of these issues. That's not to say that we don't want to hear them, rather that we encourage you to continue to use the forum to ask for feature requests and improvements to the software.
I'll try to address a few of your points below.
1) While it is possible to change settings during a render, it's definitely not recommended. Others on this forum have mentioned that you can temporarily halt the render by clicking the PAUSE button at the top of the render view window, make a change, then click the PAUSED button to resume the render. Alternatively, assuming that your computer system has the memory and cpu resources, you can run multiple instances of Terragen, thereby letting you save a scene and render it on one instance of Terragen while continuing to work in Terragen on another instance. Likewise, if you have render farm access you could save your scene and submit it to the render farm, and continue to work in Terragen your workstation.
2) We've been discussing how to implement multiple objects within Populations.
3) Animation curves...noted as we've discussed on previous threads.
4) We understand the GPU issue, but can you elaborate on what you mean by "...taking stuff out and rendering elsewhere might make sense"? Do you mean submitting projects to online render farms such as PixelPlow, or removing assets like cloud layers from a project to reduce render times?
5) Saving preview images and animation ... on the list.
6) On the off chance you haven't seed the wiki doc regarding translucency here's a link:
https://planetside.co.uk/wiki/index.php?title=TranslucencyWhile you might not always get a response for a particular feature or suggestion, we do take everyone's input and suggestions seriously.
Be assured that we're working "behind the scenes" right now on some really exciting features for Terragen.