Well if you haven't done so already I would equip the Shadow Staff and see if it has a health or energy mod on it - this will better determine if it is worth more to sell Un IDed or if it would be worth it to ID. You can do the same thing with bows and shields. Equip them still unidentified and go out in the field and see if the hit ratio is different for different circumstances or if your HP boosts at all while normal, or enchanted, or hexed. The best place I have found for testing this is outside of Sardalac Sanitarium. If it doesn't seem to have any real mods or it has crap ones, then I would personally sell it unIDed and hope to fetch a good price ^^
(but then thats just me ~_^ and I am sure some of the others around here can give you a better idea of what they would be worth)