One of the great things about sci-fi is that we can assume how things might work. There's no point trying to bring out precedence, here.
That said, combat in DW has always been very dirty, furious, and bloody. A WWII style blitzkrieg is possible but hard. Simply massing everything on the front line and pushing forward is the most viable strategy. Will this likely be the case if we are ever in space, surrounded by space empires? Who knows.
For the most part the DW universe assumes that all the races have similar ideas on morality. There are cultural speedbumps, but in the end it becomes either a galactic village or a galactic meat-grinder. This is something I rather like.
Agression Meter, though, is a very good idea. In fact, just making it easier to have complicated treaties and relations as a whole would be nice. Of course, I'd like to see a complete overhaul of the diplomatic system to something far more consequential, ala EU3 or Victoria 2. But that's likely just me.