As part of her disguise (Who me? No, I'm not a wizard! Nasty things, wizards! I wouldn't be caught dead near one!), there's a Preserver in my campaign that is wielding a spear. She's proficient in quarterstaff, so the question is, if she wields the spear as she would a quarterstaff, what penalties (if any) should she suffer?

A spear is really just a quarterstaff with a 6-8" blade on the end, so the only real difference I can see is that you can throw a spear, or set a it against a charge. If you disallow those actions, is there anything else that should be done? Spear and quarterstaff damage are the same for S-M, but spears do 1d8 vs L, where staves do 1d6.

Should I treat it entirely as a quarterstaff?