At which point I question why even bother...
I'd argue that those evaluations don't really make sense though... you can see in black and white, so why would you not be able to read?
It's not just black and white vision, though. It's
lightly obscured black and white vision.
Look, here's an experiment. A candle produces 5 ft of bright light and 5 ft of dim light. So, 10 ft away is dim light. Do you have a basement, closet, garage, or bathroom with no windows? Grab a flashlight or smartphone or tablet and your PHB and go into your bathroom (it'll be just like Sunday afternoons!). Now, let's assume your flashlight or your tablet's/smartphone's flashlight app produce the same amount of light as a single candle. They don't -- they're much stronger -- but this should still work. If you can steal your wife's or girlfriend's tea lights and try it with actual candlelight, even better. In any event, turn off the bathroom lights, turn on your flashlight, and sit it close to one end of the room -- no fair pointing it at yourself if it's a flashlight. Now, walk 10 feet away, open your PHB, and try to read.
You can't discern colour sure, but you can still see textures, you can see consistency, you can see viscosity; oil would still have a shimmer; where as blood and sewage would be obvious by their smell. Hell, blood would look black, where as water would look grey, so even sight alone would make that one clear.
Not at all. Water in a dark container would look black. You
may be able to discern viscosity, but not if the oil is something like mineral oil. Odor
might help, but if we're talking about stagnant pools of blood or sewage, you're probably not going to notice the smell change all that much. The whole room is going to be pretty indescribably rank.
Now, if indeed, darkvision is as limited as you say, and you can only really make out basic shapes; in a combat situation it's basically useless, and from an adventurers point of view it's so unreliable that you'd never use it. Even if the entire team had darkvision, you'll still have a lantern or candle to light the way because, what's the use in seeing twice as far if you can't tell the difference between a vaguely humanoid statue, and an actual person.
With such limitations, I question why it's mentioned at all. Darkvision as it's described in 3e was at least useful; and without the distinction, creatures like Drow, are stuck with the muddy situation of being up for interpretation on exactly how good their Darkvision really is.
Correct. You should basically never willingly choose to use it in darkness. In unfamiliar territory, it's suicidal. So what good is it? Darkvision is useful when the only alternative is blindness. Darkvision is useful because it turns actual dim light into
bright light.
That's the true benefit of it.
Ever notice in pretty much every D&D novel that the Underdark is always lit by fungus, or glowing moss, or magic rocks, or something? It's lit by things that explicitly provide dim light. Real dim light
isn't black and white. That means that a 120 ft passageway lit by just six candles spaced 20 feet apart is, to the Drow, a "brightly lit passageway."