Most manufacturers have touchup available for dishwasher racks, most often in approx. 1/2 oz. containers. The bottles usually come with a brush in the lid similar to fingernail polish and can be used to touchup numerous small areas.
All places on the baskets that show signs of blistering should be sanded down to bare metal and then coated. These areas have rust forming beneath the finish which will progress further unless removed.
Also available are rubber tips that can be placed over the rack tines if the pointed ends are worn and causing marks on plates. Additionally, some manufacturers make available kits that contain both touchup and tine tips.