My experiences are somewhat opposed: I find that as soon as I publicly speak about some such idea, my excitement with it will begin to vanish.

I find it curious that your post makes no mention of the possibility of the idea being right. When people first came up with the theory of evolution, I imagine it having been much like you described. People started applying it to every plant and animal and for that matter every living thing out there, and was the universal explanation for how things turned out to be the way they did. And guess what? They were right! Even more so for people who came up with the laws of physics. Yes, there is a danger if you take it too far, like if you used evolution to justify Moral Darwinism, but talking about this period of initial excitement as a purely negative issue doesn't sound right either.

In fact, I might personally prefer to extend these periods somewhat: I find that I often forget about applying such a theory after the initial excitement. Theories are declarative knowledge, but applying them is procedural knowledge, which requires practice to develop. The initial burst of excitement creates a brief time period during which you get practice by applying the theory as much as possible. After that, it might easily happen that you don't remember to seek to apply it, and therefore don't develop the skill to the point where it comes natural.

Part of higher education is an artificial replacement for this rush of excitement: I've heard several students remark that the important thing wasn't the specific courses they took or any particular facts they learned. Rather the important thing was that they learned to think like (economists/psychologists/computer scientists/Cthulhu cultists).

I'd say trying to "fight" this tendency isn't necessarily the most productive approach - instead, you might want to embrace such periods, and seek to experience as many of them as possible. That way, you'll be more likely to have a lasting set of mental tools in your toolkit, that can be applied as variedly as possible.