Though in Civ2, Polytheism gives a lovely Elephant unit that's quite formidable as an alternate cavalry until Gunpowder starts circulating.Regarding extraneous things, I'd say the following: I don't mind feathers, as long as they are attached to muscle.
A good example of good filler techs would be CIV Polytheism. If you don't go for religion, it's basically useless. But its also a prerequisite for Philosophy, Literature and Monotheism. So it's a filler tech for 7 out of 8 civs, for which you can trade if you want, or research it youself. In both cases, it's actually "built-into the real price of Philosophy".