However, the pre-FC Borg interest in assimilating life forms seemed more a means to gain the technology of life forms than as an end in itself like it began to seem (to me, at least) with the post-FC Borg. Also, assimilation didn't seem to be the pre-FC Borg's main goal in the same way assimilation seemed to be the post-FC Borg's goal.
Assimilation is beside the point. The point is that the Borg are themselves half-organic. They are humanoids with mechanical parts grafted on. Their name
is short for "cyborg." Their own consciousness consists of organic, living brains interfaced with technology. Therefore, they are aware that carbon-based organisms -- specifically themselves
-- are life forms. That's got nothing whatsoever to do with whether or not they assimilate other species. It's about their own nature as a part-biological species.
I disagree. The whole "carbon-based infestation are not life forms" idea of V'ger may not have had anything to do with the beliefs of the Machine Planet inhabitants. It may have been something V'ger itself came up with on its journey back. I mean it wouldn't necessarily be an illogical conclusion for V'ger to come to believe that only artificial life such as itself is real life. In fact, it would be quite logical. A simple malfunction in the assimilation process could explain why V'ger wouldn't accept the Borg as real life forms. Actually, V'ger would probably accept the cybernetic half of the Borg's nature. Of course, there's still the difference in V'ger's tech and the Borg's tech that would have to be explained. But, I don't really believe that V'ger was assimilated by the Borg, anyway. I just don't think the idea is as far-fetched as you do. Personally, I think it's more likely that the Borg, the Machine Planet, and V'ger could somehow be related but not necessarily directly connected.