Strangely enough I started Aikido because of the jo work, but I now use all my weapons work as aids to developing my unarmed aikido technique.
To me the boken strengthens the hip movement and extension, and teaches you to keep your hands in your centre. It also helps you to move off centre line whilst striking or using your hip. With a partner it is very useful for developing blending.
The jo helps you to co-ordinate complex hand & arm movements whilst turning and moving and, for me, develops zanshin (awareness) and fluidity. When you are using the jo to throw someone, it develops extension (and also gives you an idea of the mechanics of circular movement).
I've only ever used the tanto as an uke - and therefore in a disarming context. All the weapons are useful in this way to get an idea of miai (fighting distance).
Although I like the weapon work, and practise regularly (about 2/3 times a week) I don't think there is enough in Aikido to consider the weapons as a distinct aspect of the martial art. I doubt if I could face anyone who has done kendo or iado for even a short time, and win (without reverting to unarmed techniques!)
You ask if there are any other weapons we have used. Occasionally we used to have a 'bring a weapon' evening - so you could get used to adapting your defensive technique from such things as base-ball bats, iron bars and rolling pins.