The Sims Medieval Wiki says "Wizards use staffs of different power levels to cast spells. The power level decides along with the focus level how much chance there is the spell will succeed, how effective the spell is, and how much energy it drains." (
http://thesimsmedieval.wikia.com/wiki/Wizard) I am also pretty sure that, because they use it to meditate instead of sleeping, it is like upgrading beds - they will be better rested more quickly. So, I think it's worth it to get a better staff. If you have a higher level blacksmith, it is worth it to have him/her make the staff. A good blacksmith can make staffs that are higher quality, which increases the power. For example, a legendary quality Magical Staff has a power level of 9 or 10, while one of normal quality is only 7.