I agree with your understanding of soil pH ,and buffer pH.  The buffer pH is used to help determine how lime is recommended.  In the example you provided, where the soil pH is 5.8 and the buffer pH is 7.2, I would apply lime to that field. I would expect the soil test report has a relatively low volume of lime recommended, base on that buffer pH level. 

I have heard it once that the pH is the most accurate part of the soil test. Beyond the pH, the accuracy drops..... I think there is validity in that line of thought. I think you need to look at the soil test as getting the nutrient levels in the right ball park, not to precise manage the soil nutrients.  

And the accuracy of micronutrient test on a soil test is even lower than the accuracy of the macronutrients.  Your best bet is to use in-season plant samples to determine if you have adequate or insufficient levels of micronutrients in the plant. 

With regards to soil testing dry soils, I think there might be a bit of truth to that.  However, maybe less truth than you might fear.  There might be some variation of soil nutrient levels in dry soil, but I don't think I would avoiding soil sampling just because it is dry. I have come to the point that if it is too dry to get the soil probe into the soil to an adequate depth, then I am going to wait on some rain to help loosen up the soil. If the soil is too dry that you cannot get the soil probe into the soil, that might be part of the variation in the soil nutrient.  And I am thinking K (potassium) is the nutrient most concerned with variation in dry soils.  More so that phosphorus.   

You can google soil ph and buffer ph and find various articles to help explain the two.  Here is one article.  There are others.....

Those are my thoughts.