i think C02 can help, but like said its tricky and probably expensive to get right...

for the average grower, i think money and effort is probably better spent on other aspects, like nute ratios, soil mix etc.
with good ventilation, theres 'enough' c02 in the air, adding c02 is benificial up to a point, but IMO not worth the efort unless the other more controlable variables are tweaked to max potential