I can at least speak to one type of value-add, which is wastewater. I worked in a wastewater plant for a year as a lab tech. I even planned to get my operator license so I could stay on as an operator.

While it isn't "neglected", I would have quite literally been making $15/hr as an operator, at a time where I could have gone literally to any minimum wage job and made about that much in my area. That's not taking into account the 84-hr week you're pulling every week - 12 hrs on, 12 hrs off, 7 days (but you're on-call when you're not there). Benefits? Haha. And this was at a major metropolitan plant. I talked to a few smaller plants in the more rural exurbs and they literally were wanting to pay me $8/hr or less, with no benefits either, and they insisted that this was enough to "buy a house in the area".