Yes, of course I want a templating engine :) And I'd love to use LaTeX to produce PDFs. I have a fairly extensive LaTeX experience. And there's a gotcha:
LaTeX isn't really that good on documents where you want some absolute positioning. It is not much easier to convert an invoice form from a pretty looking Excel sheet to a LaTeX source than to a series of GD primitives. What LaTeX would make easy are justified paragraphs, anti-aliased text and the like. But, e.g., LaTeX tables are pretty awkward and there's usually a good amount of hassle in trying to convert a big Excel table to a LaTeX table.