Are there plant species that might not really thrive in the current environment but will begin to thrive once the CO2 level increases a bit further?
This depends on where you are - in the desert plants are water limited, and no amount of CO2 will help. When not near the equator plants are also water limited in winter (at the extremes they are also sun limited). In some parts plants are nutrient limited (dumping iron into the oceans causes an algae bloom - which at least short term is CO2 negative - more research needed)
Unfortunately adding CO2 only helps if there is enough other nutrients and sunlight. In the nature and forests adding CO2 is not enough. Many plants grow larger even without nutrients, but they are usually weaker in other ways and may be subject to diseases. In the greenhouses they can add nutrients and control for plant diseases and pests.
Changes in weather patterns, heat and water availability will hurt global food production.
Expect more weeds and less forests, less food and more cacti.
I saw a talk by David Battisti (Univ Washington professor). He had attended a FAO meeting about climate change and agriculture.
It looks like it is increasingly hard to engineer wheat/rice varieties that can reach peak yield with rising temperatures. The outlook for say, Indian river production, is not good at all.
From what I remember, we are currently in the temperature sweet spot for rice/wheat production.
If someone knows a primary source for this kind of thing, please comment
I don't know how much effect that will have, given seaweed is mostly it, but planted aquariums typically need to artificially inject CO2 into the water to get decent growth rates. The exchange rate with air is deeply unfavorable, so there'll be barely any CO2 in the water otherwise.
The exchange rate also worsens as temperature increases. I'm not sure how it'd work out overall.