*NOTE* i have played both the original spore and this expanson pack away from steam since i had it on a disk, and when i lost it i bough it during a sale.
I personally love this game, but unless you allready have an EA accont you wont be having much fun with Galactic Adventures.
Luckuly i had the game during its golden age, where it was a bit active in terms of more content created by players and people were discovering how wonderfully strange this game was.
Sadly maxis just left it rather than keep the game going.
I do have an EA account prior to the whole server shutdown business and can still access extra adventures, but they crash upon completion.
And without completion nor new adventures this really isn't much else than a planet scenario editor with some cosmetic items for your creature
EDIT: The custom adventures and maxis adventures work, turns out my old PC did not like them. I still cannot recommend as you will only see around 5 adventures before needing more. There may be ways to get more but i'm not entirely sure.