I grew up in a place with effectively single party rule, and it was imbued into our culture that it's pointless to vote because you'll never unseat that party anyway. A big recent change was when, in a semi-recent election, an opposition party won an electoral constituency, worth a mere 5% of parliamentary votes, by the thinest of margins. I couldn't tell you what the opposition platform was today. But regardless of the fact that the opposition still wielded absolutely no legislative power, this led to an era of what many would consider a very electorate friendly legislative push.
This "don't vote for the lesser of two evils" business is nonsense. Use your right to vote relentlessly: to punish arrogant politicians, to press on single issues, to fight for the lesser of two evils because it is the LESSER of two evils. Finding and balancing the lesser of two evils is your job as a voter.
Even if your desired choice has no chance of winning, grinding down the margin, year after year, makes the other side nervous and more willing to compromise. Even if your desired choice has no chance of losing, expanding the margin gives them more room to take less "centrist" stances and push for the things you want. If there's a lesser of two evils, keep voting until the more of two evils has no choice but to compromise and become less evil. Lather, rinse, repeat.