What i don't understand is : with such a bunch of 3D apps in your arsenal what is the project you're working on that would require Cinema4D ?
Not that it isn't a good package -it is really good for sure- but except if you're doing Motion Graphics extensively, in which case you have to consider and add MoGraph, i don't see anything Cinema4D will do that other s don't.
The other explanation would be that you don't know very well any of the apps you mentionned and then they don't fit that well your worflow ?
In any case, there is a demo version of C4D 10.5 with all the modules available and i think it would be a good idea to test it.
The last thing i'll add is that compared to XSI or LightWave, Cinema4D's render engine (be it normal or advanced...) is far behind in term of possibilities, speed and "realism".
So it all depends on what you do the most, but it's an important thing to keep in mind.
Cheers,
Laurent aka Tartiflette