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Pyroclast seems like a decent enough execution of a game from what I can see.  Assuming you were under some sort of time limit from the class.  Not sure how much level design there is in an old-school space shooter like that.  I'm guessing you set up the enemy positions and behaviors?  Hard to tell from just the pictures but a little experience in unity doesn't hurt.

 

Not sure about joy ride the video is pretty flashy without much (any?) gameplay.

 

Massteroid is awesome!  Sure it's a pretty simple game but that isn't always a bad thing.  It's a fun idea and there seems to be a good level of polish on it.

 

To get out of your rut I would focus on a slightly larger project or a smaller one where you assume more responsibility.  You don't want to bite off more than you can chew since you're working on a resume'.  Adding another finished, polished game to your resume' will be worth more than saying you're working on some awesome game.  It looks good, have fun, land an internship.

You could restrict access to new stars by having tiers of ships. Perhaps tier 1 can get you around a single solar system, tier 2 could allow you to fly around the local galaxy, and tier 3 could allow access to the entire universe, possibly thru hyperspace or worm holes. Unless you were going for a simulator I wouldn't sacrifice gameplay to include large areas of space to fly through, even if it is realistic. I wouldn't want the player to fly into empty space for more than a few seconds usually. Travel between areas shouldn't be a chore.

The story could be delivered just like you see in mmorpgs, except without other people. For example you could go around to different planets and pick up quests. To move out of this solar system you might have to do a quest from the main story line. Maybe you have to get permission from the galactic counsel before you can travel to different galaxies. Stuff like that.

Like Lord DarkShayde said, things like the scale of space and how to transition from space to planets really depend on how ambitious you are looking to be with the project. Trying to recreate even a semi-accurate universe in a video game isn't going to be possible for a while I don't think. Making solar systems procedurally could give you some content, tho it would probably be fairly generic unless you put a ton of work into it. If you haven't played mass effect you might want to check it out. It basically has a menu system that loads maps with more focus on story. If you really want the open-world aspect maybe you can have your crew periodically whine about how long the trip is taking if the player travels a further-than-intended distance. This is somewhat risky game design in my opinion and it introduces the long downtime penalty you mentioned as well, but hopefully the player would get the message and look into upgrading.