There are many ways to make a dome, and many different looks you can create by working on the aluminum's finish. On my first dome, I spent a lot of time wet sanding with many grits of sand paper to create a not-quite-mirror-like finish.
If you just want to take out the sand lines, grease, or small scratches, I would recommend using 3M 7447 Scotch-Brite 6-by-9-Inch General Purpose Hand Pad, 20-Pads
These things are cheap and easy to work with. Just rub in a circle motion. It softens the spin lines and removes blemishes. It won't be shiny, but it won't look so fresh off the spinner either.