The shutdown will likely have very little impact on the election.
First and foremost, the shutdown was over a year ago, and voters have a notoriously short memory. The Sandy Hook shootings, Edward Snowden, Benghazi: all are stories that were major political stories in 2013 that received only token mentions throughout the 2014 election.
One way to get a good idea of why and how people are voting is to poll on voter priorities. The most recent CBS polls found the most important issues for voters are the economy, health care, terrorism, and immigration. The most generous interpretation is that some of the 8% of Americans who name the federal budget as the most important issue were thinking of the shutdown. But the vast majority of voters simply aren't thinking about the shutdown.
As to why the shutdown never emerged as a campaign issue, bringing up the shutdown would have been politically risky. Polls at the time showed a majority of Americans at the time blamed the Republicans. But the shutdown was immediately followed by the botched Obamacare rollout, vindicating the most hardline Republicans who based their support on repealing the law. Neither Democrats nor Republicans had too much to gain by bringing it up.
Finally, there wasn't much of a way to personally tie too many Senate candidates to the shutdown. Of the eight RealClearPolitics tossup races, only two Republican candidates were in the House at the time: Cory Gardner in Colorado and Bill Cassidy in Louisiana. But there isn't really a way to blame guys like former Senator Scott Brown and businessman David Perdue for a shutdown they literally had nothing to do with.