Bruce, we may share certain patterns of thought, like the pull towards understanding structures. But, l've never questioned my sanity, probably because I consider the term meaningless. I generally think all people can think in similar patterns, it is just that some people spend more time in a particular pattern of thinking (some act with little pondering, some ponder a lot). If a pattern of thinking leads to a happy and content life, through the joy of contemplation itself or through the fruits of this pondering (such as better ability to relate to people), I see no reason a label such as "sane" or "insane" should mean anything other than "normal" vs. "slightly different".
Like you say, the pattern of thinking simply should not become destructive to happiness and contentment.
Secondly, unlike you I do like my mind to be constantly occupied by internal monologue, I find constant thinking/contemplation/monologue to be very enjoyable, I think contemplation is a very useful motivator. I find it difficult to motivate myself to wake up if all I have to do is work. My mind is very much cluttered with thoughts about problems I face, instead of quieting my monologue, I write and I write and I write until I get to what looks like a solution, or at least some understanding, and any emotions I may have with a statement like "am I sane" slowly fades away. I find writing to be a good aid to the internal monologue, it is slower, but thoughts flow more logically, and a solution is always found.