Yea or Nay on the Teacher's Manual?

We've been going pretty light on the scheduled schoolwork. The girls are still quite young (5 and 4) and some days when I see them playing together nicely I just can't bring myself to break 'em up and make them sit at the table with their workbooks. Perhaps next year, when Eleanor is officially "first grade", we'll have more structure, but for now I don't see it as being particularly necessary.

The workbooks we do have (math, English, and handwriting) I use by themselves, without a teacher's manual. Part of this is being cost-conscious, but I also just don't feel I need a manual to tell me how many pages a day to assign or how to teach adding or verbs. I believe I have a sufficient grasp of these concepts to be able to impart them to the young, and I assess the young scholar's mood at the time in determining whether to push on to another page or assign every other problem or just quit for the day.

The two books I have that include detailed teacher's instructions (Teach Your Child to Read in 100 Easy Lessons and Saxon 2, which I don't intend to use) have begun to frustrate me a bit. At first I found the scripted approach of 100 Easy Lessons to be helpful; now I just find it a bit fussy. Especially with textbooks and workbooks for the early grades, shouldn't the material be clear enough that someone who already understands the concepts will be able to teach it without further elaboration? Or do teacher's manuals include enough references and tips to be worth the extra expense?