I think this is in a way the soundest advice, though I have to make my own agenda clear, because it's not one most people will share, I suspect. But to me, one of the great appeals of kata is precisely the fact that they do not yield their secrets readily, that you have to work to understand the combat strategies and tactics they encode—that's what bunkai is for!—and that your reward is not a single, take-it-or-leave-it answer, but a whole palette of possible applications. Take (yet again) the Pinan kata. Yes, they've been done to death—but at the same time, I get the sense that we're just starting to recover some of the very deep thinking that went into them. I have, sitting on my desk, four separate `volumes' containing bunkai for the Pinan set: three books and one DVD. The books are by Keiji Tomiyama (Pinan Kata Karate), Ashley Croft (Shotokan Karate: Unravelling the Kata), Gennoke Higaki (Hidden Karate: the True Bunkai for the Heian Katas and Naihanchi), and then there's Iain Abernethy's DVD Bunkai Jutsu: Practical Kata Applications, Volume1). All four volumes present interesting and often persuasive accounts of the optimal oyo for the Pinan/Heians... and they're all different, at times very markedly so. I'm not a relativist in this domain; I don't think any given bunkai result is as good as any other; but there's at least a year's worth of serious research to be done in comparing just these four proposed bunkai sets and testing them out experimentally, under seriously realistic conditions (which is the only way we're going to get any useful assessment of how they stack up against each other, IMO). And there are many very experienced karateka and Tang Soo Doists on MT who probably have still different stories on how the Pinan/Heian/Pyung Ahns are best interpreted for realistic combat use.
To me, this proliferation of different possibilities, and the challenge of evaluating them against each other, is one of the great things about kata, and at the same time is a sign of something that I think is both characteristic of them and a source of frustration to many MAists (at least some of whom, I suspect, are the ones who write public hate mail to them, with OPs that begin `Why does anyone bother with kata? They're totally useless!!!!', etc.) The fact is, kata have depth. They keep their own counsel, so to speak, and you have to go to them, learn them and think hard about just what it is you're doing when you perform them, if you want to derive any benefit from them. They reward sustained study, and unlike an engineering textbook which has the answers to selected problems in the back, you aren't guaranteed anything that you don't test out for yourself. This is why you have the `fourth stage' of Abernethy's bunkai jutsu method, widely adopted in the British Combat Association: the `all-in' close-quarter combat use of the methods encoded in the kata against non-complaint attackers simulating, to the best of their ability, violent street thugs. You have to take responsibility for the real-time evaluation of the possibilities that the kata lay out for you.
I happen to like formal systems where there's a systematic relationship been structure and interpretation: the way complex macromolecular chains like RNA get translated into protein assemblies that build up into tissue, or the way natural language syntactic structures systematically map into truth conditions expressible in one or another version of higher-order logic (corresponding to the fact that a given natural language sentence has a particular range of meanings, and only those). These systems too hide their interpretation, and you have to crack their code to find the solution. That's why I mentioned my agenda earlier. I think kata are the same kind of entity: complex formal objects that are related to a set of interpretations by certain rules (in the case of kata, usually included under the rubric kaisai no genri) that you have to discover for yourself, if you weren't given the `skeleton key' by the original masters. And some of the results of this interpretation process are probably more combat-effective than others, and it's up to you to work out which those are. Kata are not easy—that's a lot of what I think is so great about them....