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.