There doesn't seem to be a lot of evidence for this? In 2012, the GOP did a huge study on why they lost and came to the conclusion they needed to court minorities. Not only has that not been attempted by the Presidential nominee, but it's failed at the congressional level too. As for third-party candidates, it's not clear what effect Perot, Nader and others have had over the years beyond helping elect Bill Clinton and W.
A large third-party vote this election is almost certainly going to be a reflection on the likability of the two main candidates, and not on their policies. Meanwhile the risk that our country could be substantially worse off in the meantime is real, and there's precedent for that.
During the primary candidates don't have the luxury of the middle - they need to find a large enough group of support that can push the party in some direction that's going to get widespread party approval while trying to find a candidate that still has a chance at winning the election.
If you don't want to vote for president then at least go vote for the many other things that will be decided that day!
Next election, politicians look at past elections. They look at what percentages each candidate got, they analyze that based on each platform, the numbers, the demographics of each state and what they voted for.
By voting for a candidate, i'm adding to the number of people that voted for them. I'm becoming part of that statistic. So i'm going to use that statistic to my advantage to get my voice heard. I'm going to vote for someone I actually believe in, even if they won't win. Then next time, at least those numbers are on the table. Maybe the next candidate will consider that by supporting "platform Y" they can get a percentage of those votes, and maybe i'll eventually have someone I support.