I see a lot of type SE and USE with age-detertiorated sheathing. Granted, it can take 20 to 30 years to happen, and materials used have changed since mine was installed, but it's a consideration. IMHO, exposed cable doesn't look as good as conduit, though I've also seen some sloppy-looking (i.e. off-square) conduit jobs. YMMV

There is industrial equipment available for x-raying things like walls and floors. It is a real PITA to use since you must figure out how to stop the x-rays that continue past the imaging area, and then deal with developing the film. The film needs to be at least as large as the area to be imaged since x-rays are actually more of a shadow technique than a camera image. A fluoroscope screen could be used (and is in newer meedical x-ray equipment with a video camera aimed at the screen using a mirror to keep the camera out of the x-ray beam) but it will need to be large enough for the images desired, or be repositioned multiple times to create a composite image from multiple smaller images. The x-ray spill must still be managed. The older x-ray film holders used lead sheet behind the film to block the x-rays, and the x-rays collimated to barely cover the film holder. In most cases there is no reason to find exactly were and what a problem is. If the wiring between two receptacles is damaged it cannot be repaired but must be replaced. A smple ohm meter can tell you if the cable is open, and then a new cable is run after disconnecting the old cable at each end. There is no requirement to remove the old cable. It is simply abandoned in place after being disconnected.

Thanks for your quick response. Basically you've described the way we have been running for the past few years. So far, we haven't had problems with the load, but I'd like to make an improvement in safety and ease of use for the tennants. My question is really about that neutral wire connection. I would like to understand why I can or cannot wire it as I've described. It should fulfill all my other requirements once installed and will be able to support a larger generator in the future.

Why not call the POCO and tell them exactly what you are installing? Then they can make an informed decision on whether their existing wiring is adequate for whatever it is you are doing, and you'll know whether the total install is adequate.