Andrew,
I guess they would add nothing to gameplay in reality.
Its just that I've studied Astronomy and in reality there are very few single stars in the galaxy.
Our sun for example is somewhat of an enigma in the galaxy.
And to see all your stars perfect main sequence yellow stars is somewhat disturbing to me thats all.
An irregular galaxy would be completley random in nature.
It would include elements of all other four galaxy types.
Each generated irregular galaxy would be very different from one another.
Also Im a big fan of emmence technology trees.
There can never be too much technology in my opinion.
For example you could add rail-gun technology.A projectile traveling at insane speeds collides with a frigate and promptly ruins its day...
