Question: In nearly any field there is a number of important results which look obvious to experts *post factum* but somehow are not that easy to come by in the first place (e.g. in mathematics some important definitions look exactly like this). Unfortunately, this apparent *post factum* simplicity makes conveying the importance of the idea to expert audience (and in particular to the journals' editors and referees) very difficult. To make things worse, sometimes the author is unable to illustrate the application of the idea by sufficiently striking examples. 

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> The question is whether it is possible (and if yes, how) to mitigate this **apparent post factum simplicity** in the talks and research articles, i.e., what can be done to *adequately* convey the significance of "post-factum-obvious" results to the audience and, in particular, to get these results to the journals they truly deserve?
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I am particularly interested in the advice applicable to mathematics/mathematical physics but the suggestions suitable for other fields are very welcome too, as the situation in question does not seem to be all that field-specific.

Answer: 
The best approach may be to address the issue head-on: include a paragraph in the cover letter, in the introduction or discussion sections of a manuscript, and explicitly in the conclusions section of a talk, that sets up a "straw man" critique. Something like: this result may seem obvious because of (expectations in the field; the beguiling simplicity of the final proof; the incorrect assumption that the problem was already solved; etc). But actually that assumption is flawed (and say or show why). Our result is not obvious because (state reasons).
I have first hand experience with this and can say that it depends on how you present and apply the findings. I recently published a paper where I derived from first principles a relation showing how a property of some natural systems varies in some conditions. The corollary of the mathematical relation where just the well known facts from Nature, except one, which was surprising. The relationship itself looks obvious when one sees it written, and this was noted by the reviewers, but they appreciated how it was presented and the fact that it provided some sort of consistency and logical framework for the observed facts.

So, in my opinion, go ahead, make a nice case on why your findings are worth publishing: examples, relations and some sort of harmony.