When a Litvak asks Rav Elyashev shlit”a for a bracha or to daven for him, he too – like a Chosid – is asking for him to be an intermediate with Hashem.
As far as segulos are concerned, aside from finding them throughout the Seforim, we find it in the Torah itself. Like arichas yomim for Shliach Hakan (and Kibud Av).