I think that anno. scale is the best way to go when using model space and layouts.  If you don't use anno. scales then you will have to set up layers with dim. styles, text styles and leader styles, one layer per each viewport scale.  As you can see this can, and did in the past, get out of hand.  Needless to say the countless switching between layers with different styles is time consuming.

It is a good ideal to setup a template with the annotated text, dimention and leader styles that you want to use.  Make sure that they all have the the annotated switch to on.  Thats all there is to it.  Now, when you first start a drawing using the template just make sure the the scales are in the same in the model and the viewport of the layout.