My understanding is as follows:
The PS says it is an optional addition because it is optional for RDA itself. RDA is used by many communities outside of LC and the PCC and each can come up with their own rulings for the various options.
But if you're contributing to the Name Authority File via the PCC of which NACO is a part -- then the LC/PCC practice at at 126.96.36.199 is indeed required and you must add a birth and/or death date [if known] to a new AAP even if not needed to distinguish between access points.
Adding dates in the 046 is useful for machine processing but does not override the requirement to record them [if known] in the AAP.
Regarding emailing creator/contributors -- I certainly don't email them all. Sometimes I can readily ascertain dates from various online/print sources, but if it is not known, then I do not record it. Once in a while though when a person has a very common name and their contact info is readily available, yes I'll e-mail them.