Shooting without hitting anything raises rogue experience? I never knew that.
Anyway, as far as I have noticed, characters' attack does not change from being weaponless, although it still is stronger than being weaponless. I don't know if it's a bug, but it's mainly noticeable with the Valkyrie Bow, which shoots a fireball and can do some decent damage and has amazing accuracy in the Opin woods areas, mainly. I also found out that it can actually hit the ghosts in the White Tower, but you shouldn't expect to count on it... My Ak'Shel just happened to actually do some damage (and even 2-3 final blows) with that weapon while he was otherwise on healing duty in there.