Based solely upon the pictures that you have posted, I would say not to worry about it. What does it look like underneath, now that is the $150 question? It could be 95% rusted-through in spots, from the underside. No amount of new paint on the topside will fix that.
If it's solid underneath and you are trying to maximize its curb appeal for resale, then I'd say go ahead and paint it. But if you plan on keeping it to use, why bother? The topside rust is superficial and unlikely to spread unless you leave it out in the rain all winter or are in a coastal area with salty air.
