I don't believe if the you can diagnose the condition of an o2 senser fron its looks because everything they do is inside. How many miles on the rig anyways, they like to go if there is any age on them. For the plugs, they will look oily black looking and they will smell bad. A good plug should be clean and should bairly smell at all, Take some pictures of the plugs and send them along i would like to take a look at them. Oh and believe it or replaicing the O2 sensors is actually part of doing a tune up! i would do them every 50k miles to keep up gas miliage and so that they don't quit at the wrong time!
I will post some pictures of my current project, 1990 range with bad bad carbon in the cylinders!