I want to make a plant based character, but the plant shape 1-3 spells allow you to do very little or grant very few abilities. I was looking through the plant creatures in each bestiary's and the spell offers access to very few of their abilities. Is this errated anywhere or is there a fix for this or has it ever come up?
Well, you are correct - plant shape is generally inferior to beast shape and monstrous physique. However, there are some very notable exceptions. You might check out Tarondor's Guide to the Pathfinder Transmuter Wizard for some ideas.
Specifically, check out:
Medium Plants - The fungus queen, mi-go, weedwhip and especially the green man.
Large Plants - Alaraune, crypt flower, shambling mound and viper vine.
It isn't about abilities - it's about number and type of attacks.
Also, the Green Man is over the top ridiculously powerful. He justifies plant shape by himself.
I've always liked the Regeneration 5 from Plant Shape III (lvl 12, 10 with some archetypes).
Edit: Cactuar (saguaroi) if you're curious.