Specialize or Generalize - what to do with a blog?

I've been debating with myself as to what to do with the blog.

That the blog will be more fully integrated with the site as a whole is pretty well a given. However, considering the variety of subjects I wish to address, should I branch out into multiple blogs or would a single blog with suitable category divisions suffice?

In favour of multiple blogs is the search engine perspective. As there would be a tighter cohesion of the topics discussed and the keywords for inbound links, each of the multiple blogs would likely rank higher for their respective topics than a single blog covering a wide range of issues.

However, multiple blogs may be too unweildy, confusing, and ultimately dilute the overall brand. When topics cross-over, as they no doubt will, just how is that to be handled?

A single blog has the advantage of simplicity and uniformity. Simplicity in design, simplicity in execution. A one-stop shop for all the writings, information and discussion.

But do I risk limiting the audience by the wider focus? If someone is reading for my discussion on issues of public relations, will they become bored if I start discussing web page design? Will someone who begins reading because of a discussion on the technical details of RSS be willing to stick around if I move on to discussing the role of a corporate communicator in relation to the board?

I feel there's a great intersection of many of these topics, but will the readers feel the same?

And back and forth I debate with myself.