From a strategy-game perspective, open space can serve as a buffer between my territory and that of other factions. I'm not sure how the proposed map and travel system for GCIV will change the feel of proximity between factions--it may have little practical impact or it might make everything feel too tightly connected.
My hope is that there will be enough flexibility in galaxy setup options that those that want virtually no in-between space can have that, and those that want some emptiness can have a measure of it (obviously within the proposed clusters).
From a non-strategy-game perspective, I really like when content creators use empty space as an opportunity for character and world building. I think Star Trek Voyager has a fair bit of this, as well as the Battlestar Galactica reboot (never seen the original, so maybe that, too), and many other films, TV shows, and games in which important plot and character developments take place between geographic points of interest.
I'm not sure how such an approach could be brought into a 4x strategy game without making the game feel terribly slow, too tightly focused/overly micromanaged, or entirely different in terms of gameplay/genre.
Also, you can use this idea, to justify a technology improvement in drives, revealing "new" star systems connected to the game map.
I like this idea in principle--having new access to locations previously inaccessible because of better technology--but I don't know if I want to discover new stars because I'd wonder why my telescopes and whatnot couldn't see them before (unless the new map locations are in different galaxies or, for example, a globular cluster relatively nearby to the primary galaxy). To me, perhaps this is a way to represent how better drive technology interacts with life support to impact travel distances--better drives means you can go further, faster, with less life support/supplies, thus opening up new systems to explore.
What this brings up, to me, though, is how does exploration work in this new map system? Do you explore the local cluster (I'm assuming it is big enough to spend some time investigating), and then go to another nearby cluster via hypergate? The doodle Frogboy showed didn't seem to distinguish distances as a factor between clusters, but I'm assuming in actual implementation, you would be jumping to adjacent clusters only, thus requiring multiple jumps to get to a more distant cluster...