I think this NSA thing could be a big issue in 2016 as it is something where the candidates will disagree in both parties. The liberal wing of the Dems and the libertarian wing of the GOP are both opposed to it. If Hillary runs I imagine she will support it and someone from the liberal wing of the party can use it to differentiate like Obama used her vote for the war in Iraq.
Partisan voters have shamelessly reversed themselves on government spying with the party change in the White House. Republican voters who, under W strongly supported government spying, now that Obama is president, support it less than Democrats do, who largely opposed it under W. That swing probably helps Rand Paul with the base while at the same time motivating the neocon wing of the GOP establishment to keep Paul from getting anywhere close to the White House. As Morden points out in another thread, Paul has the potential to win Iowa, New Hampshire and Nevada but still lose the nomination ( I predicted Romney would make a run at that move in 2012). And I think this NSA story makes that scenario even more likely for Paul, both by making early state wins more likely for him and making party elites even less tolerant of the idea of him as nominee.