>But doing so I, of course, broke all the existing code we already have, so I'm up to serious changes. That would be an opportunity to re-visit code I've written and optimize while looking at it.
And that is exactly why you should not bother trying to over-optimize a bit of code. Once everything is working fine and then tests reveal that you really really need to somehow squeeze a millisecond from somewhere, then you can look again at this piece of code, at least that is what I would do (and I know that Mike Y. is gritting his teeth while reading this:)).
"The five senses obstruct or deform the apprehension of reality."
Jorge L. Borges?
"Premature optimization is the root of all evil in programming."
Donald Knuth, repeating C. A. R. Hoare
"To die for a religion is easier than to live it absolutely"
Jorge L. Borges