I was diagnosed in 1996 with a small, asymptomatic parasagittal meningioma. Should I be getting periodic mri/cat scans or just waiting for symptoms?

Yes. Even though meningiomas are benign slow growing tumors they can definitely grow. Waiting for symptoms to occure may result in the tumor being discovered when it is much larger. This will make any type of treatment more difficult.
Periodic scans. More frequent exams after 1st discovery, then less frequent if no chane is noted.