Arijharn wrote...
Could it be that what you're getting at is their respective 'paragon-ness' or 'renegade-ness'?
No, the pairs of opposites are: the heart and the mind, traditional and progressivist, religion and science. We have a tendency for the former of each pair in Ashley, and a tendency for the latter of each in Miranda. They are both strong women, but even the ambition they share has a very different slant. Or could you ever see Ashley make her way outside of the regular military, say as a merc or in a paramilitary organization? Or Miranda in the Alliance Navy?
As for their Paragon- and Renegade-ness, Ashley can be quite consequentialist, and she has one other quality often associated with Renegades: distrust of nonhumans. Paragon does seem to fit Ashley's side of my pairs of opposites somewhat, but Renegade as shown in the game doesn't necessarily fit Miranda's.
Changing the subject a little though; I romance Ashley during the course of ME1 with the same sort of inevitability that I find myself when I come to ME2 and finding myself romancing Miranda. But I guess I'm ruthless, because I sacrifice Ashley on Virmire because while I like her:
• Kaidan is a superior officer.
• Kaidan is a biotic.
• I always put her with the bomb by some accident of fate (because I never really pay attention to the part where you choose 
Yep, that's the decision my main Shepards (femShep and maleShep) also take. But I do things differently in my ME1 playthroughs. I don't want Ashley to be dead in all my playthroughs. My Engineer femShep has Ashley in her core squad - Ashley (Soldier), Liara (Adept) and Rani Shepard (Engineer) are the perfect ME1 team, and I want to see the Ashley/Miranda conflict with one of my maleSheps romance Ashley, so I must rationalize the decision to spare her in terms of the mission.
I always try and look at the 'bigger picture,' but personally I hope in ME3 I run into other members of Ashley's family and want to see how they react.
I don't think they should add more family stuff than that which already has relevance for characters' existing story arcs. But meeting one of her sisters somewhere on a mission and having a short exchange with her, yes, that would be interesting.
As for the inevitability, yes, for a maleShep the path is unerringly ME1 Ashley, ME2 Miranda. I can get Ashley killed on Virmire, but I can't romance Liara with a maleShep for some inexplicable reason. I also cannot get Miranda killed on the SM. Not even to see how she dies only to reload after that. I've not even watched a Miranda death scene on youtube. I might want to do it if Miranda turns into a damsel-in-distress in ME3, but fortunately I don't believe for a moment she will.