Has anyone seen a designer's caluculator extension for dreamweaver to measure elements margins' and paddings' in a cascade?
Another option is to also use Firebug for FF:
and/or Developers Toolbar for IE:
These are not DW based but still can provide a good look (visually as well as css rules) at the various elements on the page and in a sort of cascading view... showing the base css, any overriding rules, etc all the way down into the nested elements.
I use both because sometimes the two browser render things slightly different.
I don't know if this idea is of any help to you, but I found an app called "A Ruler for Windows" that I downloaded. It superimposes a customizable ruler (e.g., switch between inches to pixels, lengthen/shorten, display vertical or horizontally) that you can position over a web page to measure size of elements and space. I don't recall if there is a Mac version, but I would guess there is.