DO NOT USE A WIRE BRUSH EVER.... unless its a STAINLESS STEEL wire brush... a stainless wire brush used with some good mag wheel cleaner may help a little...
there is no good way to polish it properly when its attached. due to the bolts because you can only get random accessibility to it to get a good, even shine..... if its dull and you want to brighten it you can use 1000 grit wet sand paper with water and just a drop of dawn dishwashing detergent to help cut the grime... it helps by keeping the paper from clogging.
it WILL give it a slight brushed finish, but it will brighten it a lot without ruining the finish..... and if you should ever take the hardware off of the boat where you have better access to it, it will re-polish to a high luster very easily and quickly.