SM, you've phrased the conundrum perfectly. I hope I'm not coming across as a whiny complainer in this regard. I am thinking in a constructive sense here. I really do love the Aliens franchise and hope that it can be saved on all major levels, i.e. films, literature, and video games.
The fact of the matter is that for all of their sheer awe and terror, the Aliens are animals, largely devoid of personality and character in the way that humans possess. Using them as a common thread among Aliens literature leads to stagnation, because they are constant. They never change or grow. Every Alien behaves in the same way as the next. Say what you will, but the series is still people based. Yes, a lot of them die off. Some are better than others, but when we as fans enjoy the series, it is through the vicarious experience of terror through these characters, not through the perspective of the Aliens.
In the classic protagonist vs antagonist sense, we have three options to choose from. Man vs other man. Man vs nature. Man vs himself. When dealing with the Aliens, it is man vs nature, and you can only have nature hit you with the same storm over and over again, before it gets old hat.
The problem then is either a lack of compelling characters, or that compelling characters are consistently killed off. It ultimately takes us back to Ripley's story. It was compelling. You could really connect with her on so many levels. Once she was killed, that common human thread was torn, and despite the Aliens being fascinating, the stories began to repeat themselves. We need to have that common thread again to give a sense of continuity. I hate to sound like a broken record, but the answer has been staring us in the face all along: Retcon Alien 3 and continue the story of Ripley, Hicks, and Newt. I am not proposing that they be Swiss Family Robinson. The more dysfunctional they are the better, but they do represent a common thread that people can relate to and don't require continuations of the core story to be hundreds of years later in the Ripley 8 reality.
Even if the trio only lasts for another 2 or 3 films, it would still allow for the introduction of new ongoing characters, and the possibility to have stories taking place within a time frame that was relate-able to the core story.