Having been through "agile conversion therapy" at two different companies and then having seen what the companies actually did several months later, I think most of the value of 'agile' has been realized. To get much more out of it, you need some combination of a more capable culture and better disciplined people.

And I'm not talking about just engineering - I'm mainly talking about customers and management.

Most of the gains come from tighter feedback loops between engineers and other stakeholders than tend to happen without an intentional effort. This works because it is simple - tell teams to talk amongst themselves every day, get feedback from customers more incrementally than you otherwise would, etc.

Most of the rest of the promised gains need better disciplined customers and managers - ill-defined specs, dropping projects to pick something else up, only to switch back a couple months later, managers who don't pay enough attention to what's being done until it is too late, etc.

Perhaps the problem is that it is a management fad aimed at engineers. It needs a v2 aimed at nontechnical people, "become competent at asking for what you need".