We used to use rattle cans on the rims, but found it did not stand up as well, took more prep and was slower. We are a small dealer, but probably move 10 tractors a month and do all of our own work, so we are always looking at ways to do things better, and to save time. We have some sheetmetal strips about 3" wide with a magnet spring mounted on one end. We have a couple of different lengths, for front and rear rims. They stand up around the rim, then we snug them up with the magnet. No taping, and no overspray, takes about 15 seconds to install. We wire brush the rusty spots with a angle head Makita, then sand the rim by hand, then spray equipment enamel with an HVLP automotive type gun. Takes about an hour to do all 4 rims, and they look better and hold up longer than Krylon. On the rest of the tractor, we try to just wax and touch up, but occasionally the chassis color will be really weathered and we pull all of the sheetmetal except for the cowl/dash, pressure wash with a strong detergent, sand a little where needed and wipe down with lacquer thinner. We tape off things that should not be painted, and remove or tape off things that should remain black (radiator, etc) we then paint the chassis with our HVLP gunback to the original color. Looks like new, but takes a few hours to do it right. We then install all new hoses, belt, filters, etc. A pet peeve of mine is companies that just hose everything the same color. Looks like they were dipped (usually in green). Some even paint the coolant recovery bottle, fuel sediment bowl etc.
I'm rambling here, but I will say that rattle cans are great for just touching up the undercarraige. I see pictures of tractors that were rattle canned, and can only say they painter is more talented than I am, becuase some look pretty good! Calpyro did a fine job. We also have our loaders match the tractor, gives it an integrated look.