I've been under plenty of cars and your suspension looks pretty normal to me. The suspension components usually come just with a coat of paint from new, but as you can imagine, they are pretty soon sand-blasted by the muck from the road. What you have there is a nice coating of iron oxide that will prevent any further deterioration of the steel.
I'd say that most suspension components, especially bushes and ball joints, risk needing to be replaced at some point, if you keep a vehicle long-term or for six-figure mileages. They aren't exactly a maintenance item like brake discs, but I'd say you would be lucky to avoid a replacement of some kind over a 10-year period.
Edit: to answer your question, I don't think it is worth adding a coating of anything. You won't increase the life of the steel components and the rubber ones will wear out first anyway.