Re: synastry, weight, points...
Hi Luxsaxon. I would say that the aspects might generally have certain weights relative to one another, but each chart and each comparison emphasise different things. For example, if your Sun is conjunct my Venus, but I am a very airy type who doesn't value my feelings, and my Venus is in Scorpio, then I may not thank you for stirring up all those feelings, and I might find it impossible to trust you. Its in my interest in the long term to look at those feelings, and deep down I may long for someone to connect with on this level, but I may not consciously experience this as compatibility. It could be the aspect that breaks up the relationship! So I would say that part of the answer to your questions is, 'It depends what you mean by compatibility.'
Also, if I have four planets in Aries, your Pluto opposite my Mars is going to be much more significant than if I have none, and a 'weak' Mars too. If my Mars is strong, then this aspect will be stronger, but how I experience it depends on how comfortable I am expressing my Mars. And how you experience the aspect depends largely on how you get on with your Pluto.
I think the fact that there has to be a cut-off point where generally less significant aspects are excluded from the equation partly illustrates the limitations of such a system. I'm not saying that these things can't be useful though. I don't know why they've left out important planets in the other person's 5th house - I would have thought that this would be good for getting a romance going, and then for keeping the playfulness alive if and when the relationship becomes more established.
I suppose I carry at the back of my mind various hierarchies of significance, for example an opposition is more powerful than a sextile, the Sun is more powerful than Mars, but when applying these to actual charts and chart comparisons I try to keep in mind the way in which the chart(s) emphasise some archetypes over others.
At the end of the day, you're always shooting in the dark to some extent until you get feedback from the native(s). Are they looking for someone to replace a missing element, or haven't they got that far yet, and are trying to find someone to live out their earth-sign planets because they identify with their fire? Etc, etc...
I've gone on a bit there, but the short answer to your main question, I believe, is 'No!'
By nature we have no defect that could not become a strength,
no strength that could not become a defect
Every chart is a dog's dinner in terms of consistency of theme