Mike,
There is nothing that one can do in a PDF file that is sized at 8.5"x11" that would prevent it from being scaled to print on 11"x17" paper assuming you are printing from either Adobe Acrobat or Adobe Reader and are using the "fit" option I described above and have set your printer driver correctly!
If you are submitting the PDF file to a direct PDF RIP, that is another story. You would need to set the controls on that RIP's (or DFE's) control panel to allow for scaling.
Typically, the page size doesn't determine the size in bytes of a PDF file unless the content is raster imagery. Making the PDF file “smaller” in such a case probably killed the quality as well so that if you scale it up in size, expect a high level of pixilation!!
- Dov