You'll get lots of thoughts on this subject!!
First you need to find out if the air makeup device that added air to your original galvanized tank is still operating, it most likely would be in your well casing below the well cap or seal.
I'm guessing that it is not working or it would have filled up the bladder tank with air, so I'm guessing that the galvanized tank is waterloged, and therefor not adding anything to the the system.
So if you replace the bladder tank with one of the same size you will not notice any difference. And you can remove the galvanized tank because it is just adding rust to your water system.
And of course you will be prompted to go to a smaller tank and add one of those Cycle Stop Valves.