If labour get in , will Sydney have a mini boom ?

Do you mean State? or Federal?

Remember Federal Labor have the negative gearing policy and the CGT policy. The negative gearing policy is unlikely to affect property prices much but might boost new properties a little, since negative gearing is officially restricted to them. Anyone who understands a bit about tax can see the negative gearing policy only really locks out low income earners from negative gearing. For most other people it will be business as usual.

The other policy to consider is trusts. This hasn't been well thought through, so unintended consequences are unknown. For example, if many investors buy as companies instead of trusts, what will that mean for land tax? Also, 2 parents set up an investment company and buy residential property, when they get too old to manage it they remove themselves as shareholders and directors and appoint their children as shareholders and directors. There are tax implications of doing this but my understanding is no stamp duty on any residential property. Could be an issue down the track.