So you're building in small pieces with frequent feedback and rapid adjustments? I hate to tell you this, but that is very similar to bespoke agile development.
I don't think you are against the goals of "agile" or against the principals espoused by the writers of The Agile Manifesto. It seems you share mostly the same goals, and dislike the pomp, ritual, zealotry, and rapacious consulting fees of the training coaches. Well, that's true I think of most people.
As a method for estimating work and protecting developers from marauding stakeholders outside the team, I think having a company-wide buy-in to Scrum for example is a good thing. It's not going to make your developers produce better software. It just gets them clearer specs and more chance to focus on delivery. They can still deliver utter crap if that's what they are capable of producing and what your customers accept.