Actually, starfish, octopus... are all bilaterally systemically.
https://en.m.wikipedia.org/wiki/Symmetry_in_biology
Bilateral symmetry has dominated since the Precambrian, before which fractal bodies were dominate.
Bilateral symmetry allows you to have a front and back as well as a symmetric set of senses. It's also genetically fairly easy. Because of this, I would expect most intelligent life in the universe to have this form. Of course, that could be a wide variety including octopi and starfish looking creatures.
Something I'm always irked by is scale. Most intelligent aliens weigh somewhere between a hundred and three hundred pounds. That's not even the norm for Earth life. We're actually fairly large creatures. I see no reason that anyone has to be that size though other than the planet they come from.
High oxygen content and lower gravity planet? Why wouldn't you have an intelligent creature that's fifty feet tall with a hundred foot neck? Even if the planet was just like earth, I don't think size and intelligence have to be coorolated. Why not a spacefaring creature the size of a house cat?
Also, the speed of our thoughts. Everyone seems to think at the same speed as us, but I feel that the reason we think at the speed we do is due to predation. We have to just be fast enough to not get eaten and hunt our own food. Cats think way faster than us, dragonflies think at lightning speed. Without any predators, an herbavor can slow way down and have glacial thoughts. A silicon based lifeform that moves a millimeter an hour may live for ten thousand years and take three days just to say hello to its neighbor.
