1) true no elections are ever 1 vote difference. But often enough there are differences of less than a hundred votes or sometimes even closer so every vote counts.
Also some parties depend on every vote for funding. Sometimes there is a threshhold for funding but in other cases, the party gets funding per vote. This funding is essential for these parties going forward. And more parties means more different opinions and Ideas. The major parties often take ideas from the smaller parties that they think will work. the more ideas around, the better chance a good one will be chosen.
2) It is true that some specific promises aren't kept. But most of them usually (contrary to popular belief) are and even if a party does not keep a specific promise, generally they keep the focus of the promise, the moral behind the promise.
3) there are several parties around, not just liberals and conservatives. Yes the liberals and conservatives have childish ads right now...use your vote to punish them by not voting for them.
4) Well I know it is the extreme and sort of melodramatic argument, but, people died in wars to give you the right to vote, couldn't you at least put in the effort for them? And if not, you can still spoil your ballot, that is exercising your democratic duty and also showing that you are not happy with the way things are currently going. 10 000 spoiled ballots would send a HUGE message to the government that something is wrong more than 10 000 people not voting.
5) Drastically change, usually not, but there are changes. As an example, 7% GST is a big change, Same sex marriageis a big change. Those are 2 changes that would have not been made had the other parties won those elections. So if you do not think there will be major changes in all issues, then vote based on one issue only, the issue that affects you the most.
6) Lost cause voting for the others...see my response on funding above. Also, when races are closer, the winning candidate has a tendency to care more and be more active simply b/c they do not want to give reason for more people to not vote for them next time.
I really Liked your comment whoever it was. Kepp em coming. These are important debates to have.