How much should I refer to an anonymous reviewer's extremely helpful revisions?
An ack is all that is needed. "Thanks to the anonymous reviewers for their suggestions, many of which were very helpful". Don't try to point out where those suggestions occur or your paper will be difficult to read. You retain full "ownership" of the paper so write it like it is the work of a single mind. The reviewer almost certainly sees it that way. 

About one time out of, maybe, ten thousand or so, a reviewer's comments are so helpful that the nature of the paper changes and it becomes appropriate to find a way to work with the reviewer as a co-author.