I find the Rick solution a bit complex, overly special and unnecessary. A wizard's staff should be a sidearm for emergencies, not a melee weapon that can compete with a fighter's primary killing tool. My preferred mechanic:
- The benefit of the staff spell is that a wizard can store mana in the staff, and cast spells while wielding the staff, and incidentally e.g. use it as an explosive booby trap or turn it into a snake if that's his thing.
- The staff spell doesn't provide any bonus to damage.
- If the staff is a small item then it's useless in melee combat, but is at least portable and concealable.
- If the staff is larger it can be used as a quarterstaff, club, maul, boomerang, spear, javelin or whatever it's shaped like. It does damage like any other lump of wood of that size and shape.
- You have to think about whether it's possible to attach a non-ferrous head to it and use it like a polearm. I think that would probably stop it being used like a staff.
- It probably should be possible to use a sword instead, and call it an athame.
All that said, I once played a campaign where our characters all had the advantages of both heroes and wizards, and we all used mauls that had 2+0 bonus damage for staff of power in addition to regular maul damage, and it was quite fun.