Eugene Debs ran for president 4 times and got only tiny percentages of the popular vote each time.
Nonetheless he not only got the major parties to adopt essentially his entire Socialist Party platform, he actually saw both of his principle platform planks, the establishment of a central bank (the Federal Reserve System) and the progressive income tax (which even required a constitutional amendment) become law.
In the 1840's and 50's, the Free Soil Party candidates had a similar long-term effect to establish the limitation, and then the abolition, of slavery. SO in the big picture, in the long term... WHO really wins?
Look at it this way: a vote for a visionary from a well-established "third" party of principles can have 16 to 33 times the lasting impact on the nation as a vote for anyone else! A vote for Debs in 1908 had at least 33 times the impact on the long-term direction the country took than a vote for the "major" party candidates, including any for the Republican Taft (who "won" - and what good was that presidency, anyway?).
Now YOU tell ME: WHICH 1908 voters saw their votes REALLY count? BIG TIME?
And as far as the impact on a particular party is concerned, it's like this: If your one vote is like one drop of fertilizer in an eye dropper, and you had to choose between giving it to a small but vigorous tree seedling and an ancient, rotting (but huge!) old oak tree, WHICH ONE IS YOUR DROP GOING TO HAVE THE GREATER IMPACT ON (and if you influence any of your friends, neighbors, family members or anyone else to vote for a particular candidate, how much impact will their votes and your influence really have)? And how much greater would the relative impact be? Especially when you consider (and YOU'D BETTER CONSIDER) the viciousness of all the restrictive, unequal ballot-access laws (which CAN make any one vote crucial to future ballot access for a third party). Don't you think those people who can and do THINK LONG-TERM should be the ones most encouraged to (and able to) vote?