Pashuteh Yid: Sorry, I thought when you said menchlichkeit, you were only referring to bein adom li’chavairo. If you want to extend menchlichkeit to bein adom li’Makom (ie, doing all the mitzvos out of hakora hatov to Hashem, etc), then I would have to agree this is definitely one way of looking at the Torah.
However, while doing Avodas HaKodesh out of menchlichkeit is indeed quite commendable, I do not believe it is the highest level of serving Hashem. I was always under the impression that the highest level of service is to the mitzvos for no other reason then because Hashem said we should (although off the top of my head I can’t think of a source for this).