Ok I just want to make sure it is clear. IF you DO NOT inject CO2 then surface agitation helps replenish both CO2 and O2 if levels drop below normal levels. If you inject CO2 in any way then surface agitation is your enemy because it will gas off the CO2.
As for gas exchange, surface area is the best friend for gas exchange. A minimul amount of air is absorbed by water from an airstone even if you are pumping massive amounts of air into the water. The surface area of the water, which can be increased by 5-10 fold with surface agitiation, is where most gas exchange takes place. The amount of O2 and CO2 that wants to be in the water is determined by the water chemistry and temperature.
Is why when you inject CO2 you need to make sure that the CO2 gas is in contact with the water as long as possible before it reaches the surface. O2 is the same way. If you really want to increase the levels of O2 in your tank then you would need some sort of gas reactor for O2 just like you would for CO2.
The best example I have is in summer when the wind dies down and there are no waves on the smaller ponds. This is when some of these ponds can become stagnant and utlimately completely lose all the oxygen in the water killing most life in the water. If thw wind blows then the surface agitiation will allow for faster gas exchange and higher O2 levels. Is why as long as river flows it can not go stagnant. Fish farms will run huge fountains to agitiate the waters surface and help in CO2 absorption.
I know my explanations isn't scientific but I hope it helps.