I think it is great when Christians enter politics in response to a sense of call and when they have the ability to contribute positively to society. In a democracy it is vital that Christians play a role. I am not sure about 'Christian parties' however.
What makes a party Christian? Is it because they are all confessing Christians, pray over their 'ministry'? Is it because they seek to bring Christian morals to society? Is it because they stand for the poor, working to see the government reflect the social justice dimensions of Christ's ministry? Is it because they believe in creativity, innovation and the restoration of society to God's ideal? I see great confusion among Christians in politics.
I am not convinced that Christian parties are the best way to go. Why? Because I don't believe parties can be Christian? They can reflect Christian values and seek to bring God's love, justice, ethics and hope to the world. But I am not sure they are Christian. Such parties isolate Christians and tends to see them marginalised from power unless they can become substantial. I would rather see them in the mainstream parties and being salt, light and leaven to the world.
Recent events also speak against 'Christian parties'. There is the Graham Capill disaster when the 'Christian' moralist was busted for sex offences! Then there is this in the herald about the split in 'United-Future' where we see the parties Christians splitting! How can such 'Christian' politicians stand before the nation for the values of the faith when they can't work together. Check out http://www.nzherald.co.nz/topic/story.cfm?c_id=500818&objectid=10461328.