Well, yes there will be horror stories of contrast creating reactions, but they are not co common. An average man usually can undergo the contrast MRI without
any side effects. Also, it provides very useful information about the brain structures, tumors, infarcts etc which could be missed on simple/plain MRI.
Headaches after a brain injury can also be due to concussion, and normally CT and MRI are normal. However, yes, MRI should be done to rule out brain injury as the cause.