> Your vote may not matter, but the act of voting does matter.

I don't even believe so.

Consider someone who has no family nor friends, and lives isolated 50 miles from the nearest village with a voting urn. Her vote has no social value. Does it have no importance at all?

Your vote matters, as long as it's counted. Thinking in "ceteris paribus" terms concerning votes is completely ignoring the collective nature of voting.

Even if the final count was to have a single vote difference (say 1000001 for X to 1000000 for Y), all the ones who voted for X are as legitimate as the others to claim to have "made the difference". So even in that edge case, there can be no one to be held "responsible" for the collective decision, and all of these votes did matter in the same, unmeasurable, amount.