1. The battles between ships/fleets can be watched and tracked (as in, you can see what damage is being dealt to each side as the other attacks), but the invasion battles are a simple animation screen that is based more on your 'number-crunch' representation.
2. Each expansion builds on the previous, with some things added and some things nerfed or enhanced. I can't think of anything that DL has that the expansions don't have, but some things change with each expansion (like economics, or the equations that determine the winner in a space battle, espionage abilities, trade, etc.)