Earning decent income is not a question of quantity - it is a case of quality. In order to draw traffic to your hubs, you must have quality material - hubs that people want to read. The hubs must deal with issues that people are interested in and written in a way that people want to read them.
You can write 1000 hubs; but, if no one reads them you are not going to have much of a following and your earnings will be minimal or non-existent. Some of the reasons people don't read hubs are: they aren't interesting; don't carry much content; are not written in a user-friendly way; have too many grammar and/or spelling mistakes; too technical; or one of many other reasons.
A smaller number of well-written, involving hubs will earn more than a larger number of hubs that are just slung together.