[A]s best I can tell unicameralism works fine in Nebraska, Denmark, the Netherlands, etc. Everyone has strong feelings about Israel, but nobody seems to think that adding an unrepresentative upper house of legislature would solve anything. De facto unicameralism works well enough in Canada and the United Kingdom, but having rendered their upper houses basically powerless both countries face a lot of on-again, off-again pressure to make them less silly.Nebraska aside, there's just not much to be gained in comparing the American Congress with most parliaments, because their functions within their respective political systems are just so different. Generally, in a parliamentary system, the role of the legislature is to choose the government, and then pass the things the government proposes until the next round of elections and/or such time that the government no longer commands a majority. The American Congress is, on the other hand, a transformative legislature; it is (at least) as responsible for actually writing legislation as is the president and his or her administration.
(Yes, this is to some extent an oversimplification...last time I tackled this topic, several commenters objected that a legislature that they were familiar with was not just a rubber stamp. Objections noted, and more objections welcome, but nevertheless the general point still holds).
Now, that doesn't necessarily mean that bicameralism is necessary in America, but only that it's not really useful to compare Congress to the British House of Commons.
As for Lowery's piece, I think it's a very useful exercise to think about imaginative alternatives to geographically-based representation; it's good to remember exactly what things in a polity's institutional design could be different, and the consequences that flow from choices that were once made. I tend to like geographic representation, however. Even in the 21st century, or at least so far in the 21st century, geographic areas still have an enormous effect on our day-to-day lives, and in an enormous nation of 300 millions and dramatically differences by region and area (yes, even now) I think it's very good institutional design to leave plenty of influence for particular and narrow interests. More to my tastes, when it comes to alternative Senates, are these maps that split the nation into fifty "states" with approximately equal population, from fakeisthenewreal, courtesy of James Fallows. This sort of thing preserves one of the ideas I like about the Senate, which is (contra Lowery) that the large "districts" allow internal differences, unlike House districts that tend to be more homogeneous. Both types of districts have their virtues; one of the things that works will in the American Congress is that both sets of virtues, representation of homogeneous and non-homogeneous groups, both have a place.