There's really no point trying to convince people with your mindset, but here's one more try:
Deciding the winner of an election is not the only way your vote "counts". Being visible is another way it counts.
None of the mainstream parties are driven by any rigid ideology; they shift their platforms to ensure they remain in power. If in your riding, say, a LPC candidate wins or retains his seat but the poll number show a significant increase in CPC votes over last election, he will - completely in the interest of self-preservation, admittedly - tailor his behaviour to reflect that reality in his constituency. Of course he is bound to a degree by party policy, but that's why elected MPs cross the floor or go indie.
All these parties have actuaries and analysts who "read" the overall climate of each riding.
If for the sake of argument that guy wins your riding with a wider margin because conservatives like you "don't bother to vote", he's not getting a clear picture of how many conservatives live in his constituency. He assumes the majority of voters are left-of-centre.
But... If he just squeaks by by a few thousand or a few hundred votes because conservatives get out and vote like never before, that gives him something to think about, if he wants to keep his seat for more than one election cycle. If these guys see a threat, they respond to it. And very few of them are so principled as to stick to their ideological guns if it means losing their power.
So put simply, if there is indication of a blue wave building - even if it doesn't immediately change the power structure in Ottawa - it can have an effect on how the ruling party/parties behave for the next cycle.