I think we're starting to see all the various ways the market can completely screw up the relationship between price and value (in my definition, that being how much an activity contributes to the wellbeing of society). See, for example, the lack of pollution pricing or the insane low price of meat. If you view value as something external to "whatever the market decides," the market is a terrible way to create a hierarchy of value. Why do CEOs get paid so much? It's not because they're contributing the most to society.
It should be very obvious that raising children well or taking care of the elderly are hugely valuable activities, yet the market almost completely ignores them.
I agree that pollution pricing is a good idea, and that meat may be over-subsidized. I think those have to do with corruption rather than something intrinsic to markets. Regardless of what system is in place, corruption will always be a problem to reckon with.
And yeah, raising children and taking care of the elderly are certainly important. I know that in tech cities that childcare can be very hard to find and incredibly expensive, so maybe it is becoming more valued? But the key is that the value of the service itself is not based solely on how 'important' it is, but also how many people are performing it and how much is needed (supply&demand). Or maybe a better way to say is that importance is also a function of supply and demand. Take oxygen, for example--super important, but I'm not buying tanks of it.
Software development is pretty hot right now, but if almost everyone in the world were trained to do it, the price of that labor would be quite low. This is another feature of markets--it helps to allocate resources (jobs) to what is needed at the moment. With UBI, I think you would be missing out on that to a large extent.
It should be very obvious that raising children well or taking care of the elderly are hugely valuable activities, yet the market almost completely ignores them.