Hi Francesco,
I think you should start a new thread for the "Accidental vs Essential dignities", since this one is specifically about Orientality. However, as it happens when people are really interested in these topics, threads derail naturally into other subjects, so I'm still going to reply in this thread.
In "
On the Heavenly Spheres", a book which I highly recommend, the authors mention that the Essential dignities measure the
quality of expression while the Accidental dignities measure the
quantity of expression. So, while the essential dignities concern the essence of a planet, the accidental dignities reinforce or prevent that expression.
With that said, I do follow a systematic approach for my interpretation. For instance, I wouldn't interpret Mars or Mercury alone, but I would consider them mostly while interpreting the life areas for the houses (in the signs) they rule, or if they are in one of the houses for which I am doing an interpretation.
So, that would bring Mercury as important when I would be delineating the first house. Why? Because Mercury is there, and is conjunct the Asc, a pretty visible position. So, after interpreting the sign of the Asc, and where the Asc ruler is (which would give me that the native expresses himself in subjects related to money or other possession [Jupiter in the 2nd]), I would then pick up Mercury and interpret how important it is to the native himself (considering the obvious debility of quality, and the positive factors of "quantity"), but only after I interpreted the sign of the Asc, and where its ruler is.
Mars would come eventually on the interpretation of the 1st house ("intercepted" sign), the 8th (ruler of Scorpio), or if I interpreted the 11th house.
I believe that a systematized, hierarchical, approach is really important, instead of considering everything equally important.. The bottom line of my message is that it doesn't matter which planet is "more important". In this chart, for instance, Mercury is relevant when you are doing the interpretation of the 1st house, but not relevant when you are interpreting the 11th house..
Jo?o Ventura