From a min-maxing perspective I have a hard time justifying forward bases, because the Influence is almost always better used buying free troops in my mind. A stack of 5 Paragon Mechs and a Techno-Prophet, kitted out with mods is really pretty horrifying.
The Plants and Scavengers don’t have as good of troops, and I flatly don’t know about the psychic fish because outside of my first game ever, they have never appeared again. I presume it’s because I am playing “Land” style maps, as my first game kind of soured me on the ocean gameplay which just felt tedious with all the embarking/debarking and virtually no incentive to build specialized ships when aircraft will do just as well and can fight on land, look at that.
But depending on your territory, it can definitely be worth building one or two forward bases in the mid game+ if you need to connect some territory for the movement bonus. Also, I guess if you are playing a version where you are hostile to all neutral factions, you really can’t use the influence for much besides some espionage. So maybe in that case you can just spam a bunch more forward bases.