You absolutely are working so hard to help your cat and you deserve a huge amount of credit for that. Please discuss everything with your vet and find out what all the options are, especially if you do go forward with an MRI.You are doing so much more than most people would do for their cat and I hate to think of you feeling bad for not doing the MRI. When really you are doing all you can.
These are the three possible scenarios for an MRI. Ask your vet what would be done in every case, or what would not be done, and how you would move forward.You will have either an inconclusive result, a within normal limits results with no abnormalities, or you could have a lesion show up in the brain or maybe even a deep ear infection with fluid etc.