Thanks everyone for heir suggestions. I have settled for now on this:
#+LATEX_HEADER: \usepackage[letterpaper]{geometry}
#+LATEX_HEADER: \geometry{verbose,tmargin=2.5cm,bmargin=2.5cm,lmargin=2cm,rmargin=2cm}%
#+LATEX_HEADER: \usepackage{paralist}
#+LATEX_HEADER: \let\itemize\compactitem
#+LATEX_HEADER: \let\description\compactdesc
#+LATEX_HEADER: \let\enumerate\compactenum
#+LATEX_HEADER: \usepackage[small,compact,calcwidth]{titlesec}
#+LATEX_HEADER: \titlespacing{\section}{0pt}{*1}{*0.2}
#+LATEX_HEADER: \titlespacing{\subsection}{5}{*0}{*0}
#+LATEX_HEADER: \titlespacing{\subsubsection}{10pt}{*0}{*0}
#+LATEX_HEADER: \usepackage{enumitem}
which does a pretty good job of compressing the whitespace overall. I'd still love to do more finetuning of the formatting but I think that's a more complex project. Unfortunately this seems to have broken mk4ht for me! which is a real drag as it's the only way I can reliably produce odt documents, which I need much ofthe time.
Does anyone know whether numbering can be turned on just in some subheadings? That would help me quite a bit...
thanks thanks thanks for al lthe assistance,
matt