"If people are disillusioned with politics, spoiling ballot papers would be a childish response. The best reaction would be to run for office themselves... actually make a difference."
Getting actually involved and standing is a better response, but spoiling papers is far from childish and is a very good option, it's far better than just staying at home and moaning that politics is rubbish.
Spoilt papers are counted, and this is good for two reasons. Firstly if there is a very high number of spoilt votes then the legitimacy of the elected candidate is questionable, and that is important. However the biggest reason is that it can indicate that there is a sizeable number of voters who are prepared to go out and vote if they can be pleased and engaged with. If you're a candidate in an area where the number of spoilt papers outnumbered the majority of the last winner then suddenly you've got a reason to go out and engage with people.
So many people get this backwards and say "well I'm not voting for any of them until they do something to please me" and then they just stay at home. Politicians will never bother with them, one more person who won't vote is one person that they don't have to worry about even attempting to please. The politicians will only work on and engage with those people who will go out and vote, who will change their votes and exist in enough numbers in an area to make a difference.
So spoilt papers indicates the exact number people who won't just vote for their "traditional" party and who are prepared to get off their a**es and vote.
With first past the post spoiling an incredibly useful and powerful right. So don't just sit at home and moan that they all suck, get out there and spoil, be counted and demonstrate that there might well be enough of you to swing an election. And don't dismiss it as childish.