By it's very nature, Congress will be dysfunctional regardless of size. Putting a large number of people of varying ideologies and thought processes together and telling them to work together to create laws for a large country is pretty much the definition of dysfunctional. The problem isn't the size, it's of a different make.
The dysfunction of our legislative branch has to do with the polarization of its members, the size is irrelevant. The rules of Congressional practice allow minority parties the ability to lock down progress if they feel there is no other way to impose their will on the majority. In this Congress, the only way to make it more functional is to vote out the Republicans who are openly dedicated to categorical obstructionism.
When I look at the U.S. Senate, I realize that the number of legislators is not the problem. It is the culture of the political dynamics. I believe that the Congress is a mirror reflection of our society in some respects. We are highly divided and there is not a clear consensus in political viewpoints. The solution needs to get through to the people who vote before it can get to Congress.
A smaller Congress won't get us out of our problems because they'll continue to make the same mistakes of spending more and coming up with "Washington-Style" ideas that don't work in the real world.
What we need is a larger Congress, comprised of more people closer to the middle class that the special interest groups cannot control.