Maybe you want Petal then - it embeds its templating language into the XML making up the document, so you can eliminate whole elements and their children. I never found it too pleasing, as it's only suitable for well-formed XML documents, but that might be a plus in your situation. The theoretical advantage is that you can edit the "sample" content within the templates and OOo will still output the attributes that make up the (Pe)Tal language. I haven't tried this in practice though.

Back when I had to do templates of Word documents, I channelled most data through Microsoft Office Document Properties, but the templates didn't have a need for fancy tables with a variable amount of rows.

I assume you've looked at using LaTeX to produce your output already - it's quite powerful but I'm not aware of whether the WYSIWYG editors have improved, as I'm content with the plain text editing.