TLIK – I am fully aware that many Segulos are mentioned by Gedolei Hadoros, including some that are in fact brought in the Gemara.
I do not profess to understand how these Segulos work. I do know that this question is discussed by the Meiri, who consistently takes a very rationalist approach. He explains, for example, that the Simanim on Rosh Hashana are meant for us to focus on what it is that we need, and what it is we need to do in order to merit that Hashem will provide us with our needs.
A similar approach can easily explain most, if not all Segulos (including all of your examples).
I do not deny, ?? ?????, the Kabbalastic side of these things, but I have a hard time believing that any of the authors who mentioned these Segulos, from Chazal on down to the present day, would sanction the way they have been hijacked.
Segulos, which were intended to buttress Avodas Hashem, have replaced it.
The Maharsha, as well, was fully cognizant of these Segulos when he commented on the Gemara in Berachos which I mentioned in my previous post. He says there that ???? ???? ?????? is intended specifically to contrast with such Segulos as ????? ?????? ?????.
The Iyun Yaakov (commentary to Ein Yaakov, written by the author of Chok Yaakov and Shvus Yaakov) states that ???? ???? ?????? is in contrast to ???? who went from place to place in an attempt to subvert the true ???? ???.
The writings of Rav Shamshon Refael Hirsch are replete with the idea that any means of trying to influence Hashem’s conduct of the world which is not based on the concept of ?? ????? ???? ????? ?????? ???? is, at the very least, in the spirit of Avoda Zara.
This is by no means a comprehensive, or even a representative, list of the Gedolei Hadoros who share this opinion. I would be surprised if it was not universally accepted.