Just my thought
There is another small dynamic that occurs with the agent/publisher question. There are some books that have such a small market that agents won't touch them. There is simply not enough money in it to bother with.
If you write books on fishing, there is a huge market for your book. If you write a book on local fishing holes in Barry's feed pond, the book may be fantastic and of interest to the 5000 of so people in the area, but would not have a market large enough to interest an agent.
Although I exaggerated the example above, you can see how the agent might not be interested. There are, however, micro publishers that would love such a niche market that would be interested. Going direct to those publishers would be a good thing.
The trick is to know your market, the people who would be interested in your book.