Is It Too Late?

I have been writing a blog on blogger for almost a year now. It is a running blog and was never intended to make money, just a way for me to casually write about running and connect with the endurance sports community. The posts all have to do with running, but none of them incorporate SEO or even focus on any keywords... it is just my informal journal. I have only about 20 or so followers and the site IS ranked in google, but does not show on page one unless you search for longtails that no one ever searches for.

Now here is what I want to do.... I will be running my first marathon this fall and would like to write a book about the experience. Now that I have been learning about SEO, and IM, I feel like I can promote the book a lot better than I could have just a couple of months ago.

Would it be too late to start optimizing my current blog to appear in searches, or will all the old "garbage" posts mess up my ranking? Should I just start a new blog now and focus on the various keywords that I need to optimize?

I also have a question that I can not find the answer to. Hopefully someone here knows.

If I change the address to my blog, will it take long for google to find the change. for example change from
oldblogtitle.blogspot.com to newblogtitle.blogspot.com