If it was possible to flat out buy 10% of the US congress with no involvement from the actual democratic process, it would be done more often. The Tea Party might be less grassroots than it lets on, but let's not get carried away. Millions of voters cast votes for tea party candidates in multiple elections, and democracy starts and ends with that fact. The best argument against democracy is five minutes with the average voter, yet it's what we have.
But instead of arguing over the Tea Party: How has Wilders caused the dominant parties in the Netherlands to collude less than the ruling parties in the US and the UK?
Basically, my thesis is that parties are mostly irrelevant. If there are important wishes in the population at large (ie. showing up significantly in polls), those will mostly be accommodated, not because of ideology, but because of self-preservation. For the 99% of stuff that we don't hear and care about in our day-to-day lives, the bureaucracy is in charge in all important aspects, and the iron law of bureaucracy[1] applies supreme.
It is a dangerous distraction that changing the voting system actually changes anything that matters.
1: http://en.wikipedia.org/wiki/Jerry_Pournelle#Iron_Law_of_Bur...