Andrew, your original question was about the influence of SSD in render times, and my opinion was based solely on that question. But crowning was talking of something completely different, which is loading time. Of course that loading time is greatly improved by SSD but loading should only be done once per render, so the impact on the total render time is not relevant, IMO.
I don't know about network render, I don't do that.

As to your latest question, I have 8GB and only once or twice did I hit that ceiling. Of course, your scenes may be heavier than mine. But, when my Vue is close to that limit, even though it's not using any swap file at all, I already notice a sluggish behavior, everything slows down a lot. It seems to me that Vue has so many things to handle that, although all objects are in memory, the programming algorithms are not optimized enough to handle such vast amounts of data. Or my CPU is not fast enough (I have a quadcore, Vue benchmark 100).

So, as conclusion, I would say that if you have a very fast high-end CPU, you could increase the RAM above 8GB but if your CPU is "normal", then you don't need to spend that money because Vue will slow down to a point where you can hardly work, before RAM is completely used.