Tom D.: I think I know those lightweight dowels you're talking about. The one I bought some time back wasn't balsa, but didn't weigh much more, and wasn't any stronger. It had a much smoother finish, and a harder surface, but almost no structural strength. I bought a one inch dowel to fix a broken metal-tube broom handle at work, and the dowel broke the first time we used the broom.
The second one I bought was spruce. It lasted for months, until someone lost, stole, or moved the broom to another department.