Re: spoilt vote
I agree that spoiling your vote is a valid expression of an opinion.
However, you can be sure that the extremists on both sides will not be spoiling their votes. As fewer and fewer 'normal' people vote, the extremes get stronger and stronger. I don't mean traditional political left and right. I mean fascists, nazis, communists etc. Britain and Continental Europe has been caught like this a couple of times already - BNP, Le Pen etc.
I'd rather a dull, grey FF & FG dominated Dail, to one run by Justin Barrett and Joe Higgins and a throng of single-issue independents. That might be entertaining, but as we rapidly lost jobs and freedoms the fun wouldn't last long.
For all the faults of the main parties (too many to list here), we live in a stable, safe and wealthy democracy. It's too valuable to let it drift away by abstaining from elections.