Well, see, celeriman, AGI is based on a scripting language, so it's portable to any platform for which an interpreter is written. I don't know about those others. How portable are they?
Truth be known, any of us with enough time and work, could produce an engine specifically optimized for adventure games that would be technologically superior to AGI or SCI. There are plenty of projects like AGAST, AGS, ROBOT, etc. that you could use as well.
For me, AGI is as simple as possible and holds a certain nostalgic value. I also seek to make the best game possible using a limited engine. Robin Gravel does similar stuff, as does Jen's Quest. Of course I could have a game with 16 million(?!) colors and high resolution, but I'd rather practice until I can make a game in b+w with pixels the size of melons that is still fun to play.
BTW, If you need a story, first examine your setting (space, good start). Then consider the theme (Comedy, drama, romance, space opera, etc.). Then you can begin building the world in which your characters will live. Develop some kind of conflict or conflicts that will speak emotionally to the player. Place your characters within the framework of the conflicts and their innate character will often make it easy to determine what they would do in a given situation. ROCK!