Lower fuel costs affect the economy in a couple ways. One, more discretionary moneys for the consumer increase. When the consumer starts to spend, investment grows, plants are built, jobs are created, more people have money to spend on other than the necessities of life. It's a circle that can turn into a spiral which then can, depending on the growth rate, cause economic growth until too many people become enamored with the growth, over heat the growth and then we have recession, possibly depression.
Secondly, lower shipping costs means slower increases in retail costs, which means income has a chance to catch up. Raw material prices stabilize which means manufacturing costs even out (until wage increases are demanded), truckers, railroads, airline and ship transport costs flatten out. Some of these costs may even shrink.
All of this creates the feeling, real or imagined (don't discount imagined well-being), that life is better, purse strings loosen and the economy starts to grow. When this happens governments and the market will endeavor to keep the lid on inflation. Soon, there will occur an imbalance and the markets will correct and the economy will go nuts again. Rather than let the markets self-correct government, in an attempt to garner credit and therefore votes will, in their always ham fisted manner, step in and cause further damage. Then we all have to wait for economic forces fix the problem while listening to politicians claim credit for any improvement. It's the nature of the beast in a free market environment.
Once again, I do not believe that higher taxes on tobacco products have as much impact on the shrinking tobacco market as does early training in schools, on TV, etc. does. Nor do I'm totally discount the existence of a black market in the immediate future. But, the black market needs demand and profit from that demand to exist. I believe tobacco usage will continue to shrink until there is only a very small profit incentive, far from that which is required to support a "black market." As that happens, black marketeers lose incentive to operate and become an insignificant element.
The alternative would be organized crime see profits and turns to creating a market much as they have done with drugs. Organized crime would not tolerate a black market of their product. Organized crime is much less tolerant of such activity than government is. Even the Soviets realized that they needed the black market to keep the masses content, when they couldn't deliver necessities. Which is why the black market thrived under the Communists, that market could provide whereas the government was impotent.