Well, no it is important. The first review from the University of Stirling is a review of the literature showing that plain packaging helps makes warnings more clear, packs were less appealing, and expose the reality of smoking - all causal factors to reduce smoking rates - especially amongst younger people.

The BMJ study, "Introduction effects of the Australian plain packaging policy on adult smokers: a cross-sectional study", found that plain packaging helped increase the urgency for smokers to quit. That's a causal link to reduced smoking levels.

The BMJ study "How does increasingly plainer cigarette packaging influence adult smokers’ perceptions about brand image? An experimental study" found that plain packaging helped reduce brand interest, helping reduce uptake by younger people. Again, a causal link to reducing the rates of smoking.