Yes, wider apertures = a more dense-looking field of stars. The higher you go, the more the ones that are lesser in intensity are filtered out of the exposure.
You can see by your pictures that f/5.6, and even f/11, can work just fine.
Your aperture for these type of shots should depend on exactly this, as well as some other considerations, such as what kind of exposure you will get on Earth-bound objects in the frame in that amount of time. If you want the most possible light on the Eart-bound objects, then the lower the f stop the better. As a result, you also get a very dense field of stars for these shots.