As far as sanding goes. I cant tell you yes or no without knowing how much thickness is left. With that being said. If you have enough meat on the boards you can sand each floor. If you do it yourself its hardwork. Its gonna be expensive too if you hire someone. But sanding will show you what stains will show up and more times than not you will have a refreshing looking floor after uts all said and done.

If you are simply looking for a cheap fix i dont think sanding is the cheapest.
Even if you did it yourself the price of the correct sand paper is a killer.

As far as the plywood patches in the first picture. You can feather patch those with correct species of wood ir simply leave it.

Any patching of new wood will stand out unless you stain the wood.

Harvest the bedroom wood to patch the public room spaces and then put in carpet in the bedrooms. That would let you have the best of both worlds. But, it will be very labor intensive, and you need to test the black residue as it could very likely be cutback adhesive that contains asbestos. If that's the case, sanding the floors would be out, and the best option would be installing all new wood on top of them.

There's plenty of meat on the wood, as it appears to be the original finish. And we're DIY-ers that aren't afraid of hard work. Good point on the cost side, though, if carpet is cheaper than sandpaper. That's a good consideration for the bedrooms.

What about using something like Citrus King to remove the adhesive and thus avoid pulverizing any potential hazards?

I suppose we could always harvest the gunked-up wood and use the reverse side for the patches. I'm actually pretty game for trying my hand at feathering in old to new (does that make me mentally disturbed?), since this is a cheap enough house to be a good practice canvas.

Chanes are you wont be able to use to reverse side. ( when you rip up the old you'll know what im talking about)

Feathering is tough but defintely makes fir a better look.

Get an idea of how much paper will cost you along with machine rentals.
Some machines can be hooked up to a hepa filter vac and with the right dust protection you can just sand right through all that gunk.

But good luck!

Weedy acres! I'm totally impressed that you have a floor that looked kinda like ours 5 years ago (except we didn't have black adhesive. I agree I wouldn't touch the stuff if there is a chance of asbestos). Our house had burn damage around old fireplace, chunks missing, and drywall mud/plaster. Did I mention drywall mud and more drywall mud... All over! It extended down the walls and toward the center of each room two feet. They tell you to get good knee pads for the hand sanding, but what some might forget to tell you is to protect the tops of your feet too. As you sit sanding the flooring on your knees the tops of your feet will get blisters.., I kid you not. A big rentable floor sander will do a good chunk of the work but the edges will take hand work. We stained our old red oak floors walnut. Mainly to help cover imperfections and the color variations from room to room. Looks really good. You might consider routering out an entire section of the area with plywood and lay a different wood as an accent. It's hard to tell if those areas are centered in the room. Or lay the same type of wood in a different direction. Not to cover it up just to make it look like there was purpose. Just a thought :)

Jen

Just thought I'd post a partial update. I bought a $50 wallpaper steamer like this to get the black gunk off the floors:

And it works like a charm. Here's the bedroom floor with the glued down carpet pad, after an hour of steaming and scraping:

It's slow going, but it's more tedious than back-breaking. Knee pads and latex gloves are a must!