How Much Rust Is Too Much?

Iron still seems to be the standard for a high value long lasting pump. I have an iron centrifugal that is about 3 years old that pumps good rather clear looking water from a shallow well. After it sits for a good 12 hours if I open the priming valve to let a little water leak out it is just as brown (with I assume oxidized iron) as can be. Granted this water is less than a foot from the inside of the iron pump, is this just the business as usual for iron pumps?

Is there some sort of care I should be giving this thing to make it last longer?

Sometimes I look at my all plastic pump in my pool system and wonder if iron is really the way to go... but then I remember that pool pump cost nearly twice what my iron pump did and has half the horse power.