Valuable in the sense I'm using it means the amount of compensation you can get for it. I don't mean moral value, or value to society, or any other meaning of value, just the amount you get paid. The amount you get paid is dictated entirely by how much you're worth to an employer (demand) and how easy that position is to fill (supply), which has no moral judgments in it.
I'm not saying people shouldn't do selfless things, or accept lower paying jobs that help people.
Also, jobs that have a high social benefit, their salaries are also regulated by the same forces and are not always low. Doctors get paid a lot because it takes a smart person ten years to become a doctor, and they are very much needed and provide a great benefit to society. An engineer who can design a new hybrid car is the same.
There are no moral judgments involved, you're simply selling your services on an open market.