Hardness in this case does not matter much. Durabond is un-sandable (if you try you will damage the wall around the bulge you are trying to sand away) for all intents and purposes. Just like plaster. Real plaster was NOT sanded for flatness. It was tooled before it finished setting. When partially set water is splashed n the surface (often using an 8 inch paint brush to splatter it on) and then a steel trowel used to put the final surface polish on the plaster. Easysand should be fine for a small patch not subject to damage.

Kasha_kat, Thanks for the plaster cure warning. I am concerned and will do a "test" before starting work. My brother has a paint sprayer, he did an impressive job with it in his basement rec room. Do you think thin sprayed coats would be a safer way to go for the ceiling? I have a SW nearby, I'll speak with them this weekend. Is GARDZ a BM product? Did you find Aura to be worth the price? I've not used it, although I have used some BM in the past.

If it were me, I would go low impact. You're not crazy. The charm of an old house is that it doesn't look like a new house. You just have to make your own call as to where the line is between "old house charm" and jankiness. A good floor guy can do magic to patch a floor. We have a large patched area which is invisible in our kitchen. Can you buy reclaimed flooring to match what you have from anywhere locally to use for patching, or can you salvage any flooring from any of the other work you're doing on the house? You might need to do some legwork but in most areas with a lot of old homes, there is someone. Another note...you absolutely do not need to tear out the old plaster to rewire if that is a concern. We just had our entire 1914 bungalow rewired, and in many places brought up to code, as part of a larger project. Basically the only holes to patch are where the old outlets and switches used to be, if we are not reusing them. They dropped in the new wires and left the old ones disconnected but still inside the walls. There are other reasons you might want to open up the walls, like if you want to add insulation inside the wall cavities (because of the need to install a vapor barrier, not bc of the wires), but a good electrician would not suggest it just for wiring. The vast majority of the plastering we had done was from reconfiguring the floor plan and moving our upstairs ceiling up 7". You can see the latter below. The texture of our old horsehair plaster (rough surface) does not quite match the new, but we don't expect that to be an issue once it's prepped and painted. I'm sure the availability and cost of doing blueboard and plaster varies by location, but here in Boston it is fairly standard.

I'm worried about the 'pock mark' in your second photo. A fully cured, fully ADHERED finish WILL NOT do that. You can see the centre of the pock is gone and the WHITE COLOURING around the edge of the mark = adhesion failure. I'm HIGHLY suspicious this floor is going to have more and more issues. A dropped toy should dent the WOOD but leave the finish INTACT. This is the OPPOSITE. The wood is intact (not a heavy object) but the FINISH has FAILED. I would assume the worst. If one spot fails, it is most likely it will ALL FAIL. As for the white scratches, that can be normal for a fresh finish. Even after a full 30+ day cure they can be a little delicate. I would recommend bringing in an NWFA Certified inspector (www.nwfa.org) and pay them for an inspection. They will perform an adhesion test to see how well that oil based poly is grabbing the Minwax stain. While you are waiting for the NWFA Inspector to call you back, I would reach out to Masterline (as G&S suggested a few weeks ago) to find out if Minwax is an acceptable stain underneath their product. And if so, how much time they want to see from 'stain' to first coat of finish. Minwax is KNOWN for taking many many hours (some required 24-72 hours) before the first coat of finish can be applied.