Spell question
 

Does fungi staff clickie, (fungal regrowth stack with the regen line of spells?

No. Stacks with worn regen, though.

Which is better, the staff buff or regen spell?

Regeneration is 5 hp/tick, Chloroplast is 10, and Regrowth is 15. Per the wiki, the staff clicky is equal to Regrowth by level 20, albeit with a snare component.

Yah, its basically getting regrowth early, that doesn't use mana, and doesn't take up a spell slot. Very worth it imo. The snare component means nothing, if you are in an unusual situation where you need to run, you can always click it off. If you need to run very often you have more issues than this clicky can fix.