My question is though, how do you know if the problem/solution you're working actually matters to people? Is there any kind of validation system that's worked for you?
To summarize part of the approach: you want to have high-bandwidth conversations with specific individuals who you think are part of your target market. Make sure you and they agree on the problem. Then try asking a question like "If I built a solution to X and offered it to you for free, would you deploy it?"
If the answer is "no" then it's obvious that the problem isn't a particularly high-value one, OR you don't actually have a proper shared understanding of the problem.
If the answer is "yes" then you can start trying to bound the actual value of the problem. "Well, what if I charged you one million dollars for the solution? Would you deploy it then?" The answer may well be "no", but that's OK. Now you can start a sort of a binary search process to try and find some common ground.
Beyond that, there's a series of books by a guy named Jeff Thull that I really like, which you might find valuable, at least if you're trying to sell something in a B2B setting. The first book in the series is titled Mastering the Complex Sale[2] and a big focus of Thull's approach is about how to develop a "shared understanding" of a problem, and the value of a solution. It's a "sales" book, but it's not the kind of "sales book" that's about trickery and manipulation, etc. It's really about how to work together with a prospect to gain that "shared understanding." I'm a big fan, FWIW.
[1]: https://www.amazon.com/Four-Steps-Epiphany-Successful-Strate...
[2]: https://www.amazon.com/Mastering-Complex-Sale-Compete-Stakes...
The real question you are after is, "is this problem significant enough to others that they would pay enough for a solution that you can have a sustainable business?"
You have to talk to them to figure that out.
Usually you have to go where those affected people are in order to get out of your subjective zone. When you get there you find those who are concerned and look for signs of controversy. Arguments, trolls, emotional behavior, etc.
Another simple example, but you can see people do this with Ask submissions (and their analogs in other communities): They front-load the problem with objectivity by asking others, "what problems are bothering you," "what would make work easier for you," etc.
This is how they identify the problem in the first place. A lot of them are looking to leverage the feedback into buy-in when they come back with a solution.
The approach looks simple but it does a good job of keeping the leverage side clean of too much subjectivity in the beginning of the process, so it's easier to make sure it's a problem that's not just something you perceive. (Also if you get "yeah, but..." feedback to your solution, it starts looking rude really fast, which can be the right kind of pressure when your solution is novel or requires some learning)
My problem is more like I've potentially found a way to streamline/improve this process. Concern is however will it be important enough to get users attention, let alone monetizing down the line.