i have Nitro Pdf Professional. Up until now i only used it to crop headers and page numbers from PDFs. The other day i used it to convert (cropped) pdf to RTF... Excellent results. I believe that converting that RTF to MOBI by Calibre would produce infinitely better results than straight Calibre PDF to MOBI.
I did not try it.. what i did was, I saved that RTF to filtered HTML in Word 2010. Then

i used
wordoff.org to remove all Word generated garbage from that HTML and then imported that HTML to Calibre and only then converted to MOBI. I believe what i got in the end is better than many Amazon's Kindle editions.