[giantrobot]

Stars are still sparse enough in both galaxies that most stars still wont have much effect on most other stars' planetary systems. On the scales of the galaxies a star system isn't much bigger than that system's star. A star affecting another's planetary system would pass so close it and the host star would likely form a gravitational relationship and would be considered a "collision". Space is stupid big and stupid empty.

[ProZsolt]

I really like this demo to show how empty our solar system is: https://joshworth.com/dev/pixelspace/pixelspace_solarsystem....

Or the RL version in Sweden: http://www.swedensolarsystem.se/en/