I love a polished lip, but just lost the will too live with keeping many sets clean over the years, hence i went black on my Weds, the problem is, let them go just that little too much and a machine polish is the only way to get them back, but as Ekona says, £100 or thereabouts once a year is no biggy imho, but a set of winter rims is advisable.
You could always get them lacquered (std wet spray) once polished or even clear anodised, that will protect them but take the edge of the bright finish, or if your feeling brave, get them polished and then powdercoated in a translucent colour, such as:
http://wheelsperformancecom.stores.yahoo.net/pocooulip.html