If forced to choose, I would opt for planetary strength over topical relevance. Even with 12 houses, I give planetary strength precedence over topicality where the intermediary houses are concerned. (BTW, thanks for pointing me at traditional methods for this over the last year.) Even a stellium in one house is, uppermost, a combination of planetary forces and only secondarily a concatenation of topical references. Or so it seems to me.
I don't think it's an either/or situation. We can do both but it's important that we know which we are doing at any one time. Also they're not completely separate activities. The Angular houses are the most important even in Whole Sign systems, followed in general terms by Succeedents and ending with cadents, though this is modified by taking into account a second factor, that is whether the House makes a major aspect to the Ascendant. Planets in aspect to the Ascendant gain strength.
Since my previous post, I've found something by Firmicus Maternus on the 8 House system. He was a fourth century Hellenistic Astrologer, so he's towards the end of the Hellenistic period. Also he's more a reporter than a practioner, so I have some doubts about his knowledge of this system. Nevertheless for what it's worth His topical meanings are:
House 1 - Life
House 2 - Money (and resources)
House 3 - Brothers (and presumably Sisters too)
House 4 - Parents
House 5 -Sons (and Daughters)
House 6 - Health
House 7 - Marriage
House 8 Death
The IC divides house two from house 3, the Descendant divides house 4 from house 5 and the MC divides house 6 from house 7. This makes Life, Marriage, Children and Brothers the angular houses - which is clearly a very family centred division and reflects the vital nature of family in those times (without family it's difficult to maintain life in a predominantly agricultural environment).
He doesn't give a rationale, for the system, so I suspect it's something he's come across but there's no one who he can contact who can explain it. Manillius refers to the four spaces between the angles as reflecting the four stages of human life - which is not an unreasonable idea, even to modern ears.
This missing houses compared to the twelfth house system, are the last 4, which suggests that a some stage, the MC was not identified with action or career, indeed that this was not considered important to be separately shown. I tentatively think this might be an indicator that the system was again linked in some way to the length of life calculation but that's really pure guess work on my part and I'll have to read Manillius to get more information.
I've seen claims that the references to an 8 house system are through misunderstanding and that Patrice Guinard (weblink cited above) is in a minority in his views. I'm not able to take a clear view, though a 12 sign zodiac lends itself to 12 houses - and Whole Sign houses if the '12' are accepted.
Your right that the 8 house system really only allows Conjunctions oppositions and squares, which suggests predominantly pessimistic readings - which again might have accounted for it being rejected. It perhaps also explains why those three rank above trines and sextiles in Astrological theory (because they are later additions?).