The better choice is using a 6" stitched cotton wheel like I linked below with a bench grinder. A bench grinder has 2 wheel attachments on either side. You can disconnect the grinding wheels and put in a polishing wheel instead. There are many types of grinder, basically any kind should work as long as it takes a 6" wheel. There are even versions without the housing material around the wheels which make polishing much easier. But even with the protective housing I think it will still work for you (it is what I use).
Come to think of it, the bench grinder's grinding wheels can also be used to grind away the casting defects instead of the tungsten carbide burs for the dremel. And you can buy a wire wheel for the grinder which can help you clean up the bones or other projects in the future.
This is a bench grinder. They are cheap and can easily be picked up second hand for even cheaper.