The abolition of the Seanad would effectively increase the Dáil’s power by removing scrutiny of bills.
It would also remove democratic safeguards for certain actions that require the approval of both houses, such as impeachment of judges or the president.
The power of the president to refer a bill to the people (currently at the request of the Seanad and one third of the Dáil) would also be removed.
Fine Gael’s claim of savings of €20 million is dishonest, and is apparently their main argument, but even if abolition could save that much, it is a small price for better and less partisan scrutiny of bills.
Their other argument for it is that there would be fewer politicians (as if that is an advantage in itself). This is populism and not a real benefit: The alternative to politicians is dictatorship.
See the full list of changes:
http://referendum2013.ie/Constitution_Before&After_Seanad.pdf
The full Green Party / Comhaontas Glas position is available in English and Irish on www.greenparty.ie