If bitcoin became a legal currency, many people will notice bitcoin and start using bitcoins. It will give a good impact into bitcoin for sure and the price of bitcoin can increase.
More and more people will start using it, yes. But a "good impact" may not be a good way to put it because we can't know for sure if being popular is beneficial to the bitcoin industry.
Being popular is for sure beneficial for bitcoin industry as popularity brings investments and investments decides if where bitcoin will go, the more its demand increases the more its price will increase as well, suppose you have 1 bitcoin and there are 5 people willing to buy it, wont they try to win it by bidding higher? That would be the case with bitcoin if it gets more popular
It all depends on what those 5 people are going to do with your precious Bitcoin. If they are competing for it with the purpose of reselling it to the rest of the gang, someone will necessarily be left holding the bag in the end. And Bitcoin will be of no more interest to them any longer since they have all used it (or tried to use, lol) as a vehicle for speculation and profiteering...
This form of popularity is beneficial for bootstrapping a coin, but not for a long-term success of it