Thankyou, Matt. This takes us to the heart of the matter.

largely unconscious instrumental human rationality has already equipped me with a way to achieve my goal: apply butter to knife, apply buttered knife to toast.

Isn't this a completely ludicrous example of "rationality"? What does "rationality" signify in this case? Unconsious co-ordination and control of the senses and muscles? That is not what I, or any sane person, understands by the word "rationality"! Is "rationality" just a universal signifier for "doing stuff right"? The word has been stretched beyond all meaning! You may rationally believe that particular way of buttering the toast is the correct way, but this is an example of epistemic rationality. There is no need to invoke the non-concept of instrumental rationality.

I'm achieving predictably (repeatable on many trials) suitable (meeting my goals satisfactorily) results relative to my desired level of utility (buttered toast in my belly is a small but detectable increase in utility)

I'll be honest with you, I have never detected utility in my belly. I know this is tangenital, but the concept of utility just does not seem at all useful. How do we calibrate this unit of measurement? Or is it simply an abstraction? I can see how that might be useful in an abstract discussion, but in this case why not refer directly to the actual feelings felt? Saying that you "increased utility" is pointless jargon, and its use contributes to the kind of confused word-salad which occasionally appears in these sorts of discussions.

[...] In either case the basic principles of rationality could be brought to bear to improve my results, if my estimate was that the time investment of attempting improvements would be justified by my expected increase in utility.

Here's the crux of it. Your improvements will make use of the standard tools of epistemic rationality, the scientific method and all the rest of it. There is no seperate world of instrumental rationality. At best "instrumental rationality" may be defined as epistemic rationality applied to the problem of choosing among methods for achieving a goal, a rather weak and pointless category. The actual methods themselves are emphatically not a form of rationality.