The best that you can do is to read such files in landscape mode, so that the print appears larger.
Someone was working on a program called k2pdfopt that could be used to convert PDF files to another layout. It worked pretty well, but unfortunately it converted the output to static images rather than PDF, so you couldn't follow links or search the text anymore. Still, if you just want to read the file from start to finish, converting with k2pdfopt is not a bad option. Search the MobileRead forums to find the thread where the program was introduced.