Hi George, there are two approaches; to mechanically remove the tarnish layer using a very fine liquid borne abrasive like Brasso (the clue is in the name). The other way is to use a mild acid to dissolve (eat) the tarnish. I have heard of HP Sauce and Tomato Ketchup being used, also Coca Cola (phosphoric acid – very bad for your teeth), vinager and bicarbonate of soda apparently works well too. See http://uk.answers.yahoo.com/question/index?qid=20080711070456AAwJ4Kk The old brass may have a layer of lacquer to protect it although it has probably all worn off by now.
The challenge is not so much how to clean the brass but how to keep it shiny once you have got it clean. It may be that you could spray each fitting after cleaning with an aerosol varnish or lacquer, but I suspect even that will wear off eventually. Maybe part of the pleasure of owning a venerable wooden Wayfarer like yours is the regular polishing of the fittings to a golden glow. There is probably a good reason why modern fittings are mostly in stainless steel.
It is always a good idea to take fittings off when you clean them and make sure the wood under them is in good shape and that the fittings are well bedded onto the hull when you fix them back, if water can get beneath a fitting it will quietly rot the wood and one day the screws holding a fairlead or something will pull out. There are a range of sealants you can use, I use Sikaflex 291 on my GRP Mk2, there may be others more suited to a wooden boat. Don’t use a silicone bath sealant however, it just won’t grip.