Once chrome or ally has gone, you will never get it back and if they are chrome, be prepared, whatever you do for a pain in the a&&. You will need to get them dipped to remove the chrome (sand blasting etc just wont work) and then you will not find anyone willing to rechrome ally without paying an absolutely ridiculous amount and they are a one piece wheel, even harder. So your left with having to get them polished/diamond cut, no bad thing, but then you face the dilemma of keeping them clean and shiny, unless you lacquer them, which will eventually end up with the dreaded white worm as water gets under via small stone chips and it will still cost loads. Welcome to the world of wanting shiny rims
To be fair and no offence, they are cheap, not very pleasant rim and they are 20's, you would be better off living with it for as long as you can, flog them on and put all that money towards something else in a 18" or 19" variety. They are just not worth the cost of refurbing, your probably looking at an absolute minimum of £500.