If there's no bending or obvious damage then my question would be "why change ?"
You can fit heavier axles but then you'd be into larger bearings and possibly new hubs. I'm not sure on the latter but it wouldn't surprise me that the whole lot needed changing. If you want to fit aluminium hubs, different brakes, etc then heavier axles could be part of the package.
But like John, I've not heard of them being a major problem on the cars. Vertical links do break/wear but that's usually down to lack of maintenance.
Brian