I wouldn't suggest hyperlinking is going to result in more sales, or that bookmarking and hyperlinking can help make up for deficiencies elsewhere in the document. Actually, I often find hyperlinking in PDFs annoying. But I think bookmarks at the chapter level are nice, and bookmarks at the primary heading level are wonderful.
Regarding getting something reviewed, bookmarks *may* help you get your document reviewed a little sooner.
Bookmarks *may* also increase the perceived value of the document. To me, bookmarks are one of those "finishing touches" that say the company wants to make it easier for me to refer to their document often. It goes back to the discussion about PDFs vs. hardcopy and muscle memory. If a PDF has bookmarks, one to three clicks and I'm at the page I want. Without bookmarks, I have to enter the page number if I can remember it. Or, I'm reduced to scrolling to some point near the section I want, thinking where the section on screen is in relation to the desired section, and clicking several times to get to the section I want. Bookmarks give you the ability to use muscle memory to quickly get to the sections you want to read.
As far as how long it takes to add bookmarks to a PDF, I suspect that's dependent on what software you're using. As a tech writer, I've used FrameMaker extensively. It lets you specify which paragraph types (titles, chapter titles, heading levels, etc.) will be pegged for inclusion as bookmarks in the PDF document. Once you know FrameMaker, setting up the bookmarks takes about two minutes. Cranking out the PDF from FrameMaker takes about five to fifteen minutes of work, plus processing time.