Those talismans are basically unfinished content - the secret quest regarding the talismans was never made, so a secret bonus would be a novelty but ultimately rather pointless.
I think making a new quest now would also be a waste of time for both the developers and us who'll eventually play it for a quest reward scaled to 10 years ago, as all quests are.
I'd maybe give it a +Prayer bonus, so that the people who believe that does something can find a use for those items.
Or maybe while you're wearing a Talisman, the prayer flavour text is more animisticly (or another native American religion) styled, but again these are just a novelty.