The fact that Tesla has been even remotely successful is kind of a side benefit. The biggest thing they've done is transform the electric car market in the popular consciousness from being a joke. Ultimately that means that a lot more consumers are going to start considering electric vehicles when they are looking to buy a new automobile. Also it means that there are likely to be a lot more new entrants into the electric car market (both existing automotive manufacturers and new companies), because it's becoming a place where companies can make money. All of which will put the electric car market into the same sort of profit -> R&D -> better vehicles -> profit feedback loop that the internal combustion car has benefited from for over a century. One way or the other we'll find out whether the potential of electric vehicles matches the promise.