For Marina, again
You noted, " I took a look at Lilly's "Christian Astrology" (a friend gave me the PDF until I can find a print copy ) and it's very clear he does not attributes many 'meanings' to the planets, but rather a sort of influence (a well-dignified Sun makes one faithful, prudent, majestic etc., a ill Sun arrogant, disdainful, restless etc.)."
This sparse definition approach to a planet's role is to be admired. It is something that I do, yet I am not considered a Traditional Astrologer. Simplicity permits one to find clarity. Relying upon a planet in a sign and house definition from a book will yield several or many pages of words. All of that crap is useless. If talking with a client or a friend about their chart, how much of those several pages for one chart planet could you remember, how much time is availble to expouse it, how would you choose which of fifty statements to make and which to not mention? Again, simplity permits one to find clarity.
The "unifying" role of the Sun comes from seeing only those planets it has aspects to in terms of their roles and how the Sun strengthens their positive and negative or neutral roles. Once you understand that part of the chart, one might choose to look at the Moon in terms of 1) how one deals with change, 2) how the Moon defines primary needs, fears, feelings, 3) how one's past, family and women play a role in our life.
Then we attempt to picture how the Sun's attitude, vitality, decision making works with/against our Moon's needs, feelings, past and women we associate with. This often covers much of the chart. Those planets and the angles that are not involved with the Sun and/or Moon need to be looked at in a similar way. It doesn't take much to get a good initial grasp of a chart. As you work with a chart its details clarify, you reasses and change your views, and finally the ways in which it either comes together or reflects disparate portions of a personality becomes clear. Dave