"Yea" pronounced "yay" is a valid word with practically the same meaning as "yeah" (affirmative). Granted "yea" is archaic and most of the instances you are catching are just yeahs with the "h" dropped, but it would be nice to choose something that is definitively wrong. The anyway/anyways is a better choice and I hope that "anyways" does not become widely accepted because it is like Bieber to my ears.