I'd consider replacing it with a Rohn.
Those ladder-style towers are rather flimsy - as wind twists and torques on the tower, those ladder "rungs" fatigue and welds break. Those towers can go from "safe to climb and use" to "unsafe and dangerous" in a hurry. Paint hides cracked welds and flaws.
If the outside looks that bad, I'd be worried about what the inside of the legs looks like. Rust and corrosion weakens the structure from the inside out too.
If you want to clean it up for aesthetics, i'd shoot it with cold galv. I use ZRC cans.
But again, I'd be real leery of doing anything on it without knowing a lot more about the complete condition of the tower.
Also, tower painting fucking sucks... hire that shit out.
That is a job I will not do.