I use a product called NeverDull on all my wheels (bike, car, Jeep). It is amazing, can make any wheel shine! And it takes off bugs, tar, etc with little effort!

If youve let them go a while & have some
Catchin up" to do, get a strip of nylon web, like a dog leash & put a wrap around a spoke, pull tight & slip it back & forth with whatever polish you like in the mix.If you can find a single thickness web, about 1/2 wide, it will even slide between the spokes where they creoss. Depending on how you have it wrapped & which end you are pullingg it will run down & wrap up the spoke nipple & polish that up, too.