PDF files are text files with some binary fields in them, so you should be able to just open the two files in a text editor (or use more / vi / grep ) to inspect each. A file comparison tool might also help you discern whether Preview is re-encoding the assets in a sub-optimal manner.
Automator also has some PDF processing tools including compression, compression of images and rendering the pages as images. I would try exporting the resulting PDF from Preview and select the Quartz filter of "reduce file size" to see if perhaps that would reduce the size.
You can see several related questions where others have noticed this effect where the standard settings increase the size of some types of content.
As a postscript, a 35 page paper in ascii format weighing in at 950K is pretty efficient but also still an order of magnitude larger than some basic texts that are in the 60 page range even with illustrations on each page.
Take for example this book from Project Gutenberg - The Cat and the Mouse by Hartwell James and John R. Neill
- The plain text (UTF-8) and HTML versions are in the 70 kB range
- The ePub version is a sleek 45 kB with no images, but swells to 2.8 MB with images.
If I take the HTML version and inspect it in Safari, it's clear the 75 kB is just the main text/HTML file and not all the included images. Printing that page to PDF using Safari (which uses the same rendering engine as Preview) - I get a 3.7 MB file that can be compressed with Quartz reduce file size filter to 2.2 MB.
Hopefully these examples help you in deciding whether to generate all versions of your files in LaTeX or live with the libraries for PDF generation on OS X.