Best rastrize method?

Hi everyone.

Every day I have to deal with dozens and dozens PDF files: mostly, it's a kinda huge booklets about 600 mb - 2 gigs each, with lots of text an AI (or vector) illustrations. The final goal is to get a booklet where text is a text (or perfect quality) but all pictures must be rastrized, at least all massive (coz booklet may contain huge detailed illustrations and super basic icons). I've been using few methods:

1) Exporting every page as image and combie them – too long and text becomes as text.

2) Printing as PDF with "flattetning options" — I don't know why, but it skips sometimes huge illustrations, even i got a maximum rastrize/vector balance. And there is combined option for "Line art and text", so you can't it separate it.

3) Printing as image – as well as exporting every page as image.