I have two thoughts - one as I mentioned is go find a new trailer and see how the axle reacts to your movement. The second is I would look at the arms and see how they are positioned - if they are pointing up, more than 5 degrees or so, then I would replace them.
Don't know if you can tell on my 75 in the photos, but my wheels look like yours. From that they look fine - I even had a very reputable A/S dealer check my axles and they said they were fine. Mine are about 5 degrees in the "up" position. They said that there really is not much swing in the arms - perhaps 2 in or so. Also, I talked to Henshion awhile back and they said that if your getting uneven wear they should be replaced. They also said that up to 10:00 is ok and should go down to 4:00 unweighted.
Having said all of this, I think my trailer needs axles. When I jumped around in a new trailer, the difference was dramatic - much more bouncier than my (1975) trailer - mine is very stiff when you jump in it. I probably won't replace mine as I fixing up a 1958
(love those 50's trailers) and as I watch my trailer during travel all seems to be holding up well. I'm also know that my trailer sat unused from 1982 until 2002 when I bought it.
I am putting new axles on the 58 because I want all new running gear.
I also think that axles are relatively inexpensive insurance that will give you peace of mind knowing that running gear is all new with zero miles. The new axles are balanced better. I've known several who have broken spindles because of age.