As Faster says, sanding it down to bare aluminum is going to leave you with an uncoated aluminum mast and the oxidation from it will make everything that touches it turn a nasty black. Re-anodizing it is possible but very expensive as you've got to find a facility capable of taking something that long. Spray clear coats tend to flake off like cellophane sheets in short order.
Try to detrmine the type of paint that is on the mast. If unable to do so, try various solvents as used with different paint types; the one that dissolves the paint is indicative of your paint type. I do not recommend removing the paint on the mast as long as it is adhering well. You'll have as much, or more, trouble getting your new paint to adhere to the primed aluminum as you will the old paint. Acquire the same type of paint used to paint the mast previously and apply it over the old paint after prepping the old paint. You need to take the gloss off the old paint for good adhesion of the new. Feather out gouges and fill any dents, etc... as they'll show up much more after painting.
I'ts not that big of a job, the prep work takes the most time. Rolling and tipping gives great results and, with a good color, you'll wonder why you ever thought that plain aluminum looked good.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.