One argument in favour of an elected Lords is that it would have greater legitimacy to stand up to an increasingly powerful executive. Some argue that the Lords already does stand up to governments and cite the rejection of Brown's plan to bring in 42 day detention as evidence of the lack of need for reform on the grounds of weakness of the Lords.
However, in truth, the Lords remains weak. Brown could have pushed 42 day detention through using the Parliament Act but decided not to, probably on the grounds that it would bring him too much criticism. So the Lords had influence over a PM who was not interested in attracting criticism.
The Lords has faired less well in blocking many of the Coalition's reforms. The Lords had voted against many of the coalition's welfare reforms (such as the £26,000 benefits cap). However, the Coalition are a lot more willing to take criticism than Brown was over 42 day detention. The Commons just simply voted to overturn the Lord's amendments, using a technicality known as "financial privelage". They didn't even have to use the Parliament Act. So the Lords can do very little when faced with an assertive government with enough seats in the Commons to push through a law. The Welfare Reform bill became law in March 2012.
Whether or not you think this means the Lords should be reformed to make it stronger depends on one's point of view.
