I don't think they detract from any of the mystery since as I demonstrated, they don't really explain anything about the force anyway. To me they're a non-explanation.
I would have been totally OK with them if they were used purely as a mechanism for detecting and (for lack of a better term) grading force potentiality in individuals.
Like say for the sake of argument, if midichlorians were simply microorganisms that were attracted to force users, maybe even feed off the force itself in small amounts, like remora fish. So the more force sensitive a person is, the higher ratio of midichlorians in their blood stream and so they serve as a convenient measuring tool. That I think would have served the purpose of the scene and still allowed for the element of mystery.
What this new episode seems to imply is that the cosmic force itself somehow created all life in the galaxy on that planet and specifically set up midichlorians as the intermediaries between the tangible and the intangible. I sort of get it, but it still feels a bit off.
Either way, it's more than what we got in TPM and actually ties in better with the concept of Anakin's "immaculate conception." The "will of the force" is something often mentioned but never really addressed, but it does indicate that there's a form of consciousness--perhaps this cosmic gestalt wellspring that makes it so hard to maintain one's identity after death--behind certain events. It sounds just like that kind of amoral force of nature to create a being that will be both Jedi & Sith and is destined to destroy them both to restore balance AND (if you'll pardon the expression) plant the seeds of rebirth in the form of his offspring.
...But I digress.