But if they hadn't given any tax breaks at all, Tesla wouldn't have gone to Nevada. Which means that the full 'foregone revenue' was never an option on the table in the first place.
Consider the middle ground. Tesla were looking for about $500m of incentives, and got a lot more than that. Now if the projections pan out it may work out very well for the state but it could end up as a white elephant, as these deals sometimes do. Also, consider that about 10% of this is coming out of reduced incentives for other industries, who will now presumably invest less in Nevada than before: http://www.rgj.com/story/news/2014/09/04/nevada-strikes-bill...