Increase pause duration in Audiobook - can I do it globally?

No, I'm afraid that Audition won't let you do that - there is no way that you can use any form of parameters to specify pause lengths. One way you could undertake this would be initially to break down every paragraph into its own file, add a second to each (you could do this as a batch process) and then concatenate the results of all these files back together, and save that as a new file. But you'd have to do that manually, to get the breaks where you want them. Since you have to do that anyway, a possible alternative would be to create a favorite to add a second of silence at a cursor point, and each time you get to the end of a paragraph, hit the shortcut key for it. Then all you have to do is resave the file, which will be n seconds longer where n = no. of paragraphs.

On top of that, you also need to be aware that Audition doesn't deal directly with MP3 files - it has to decode them to wav files first, and if you save your result back to being an MP3 file again when you've finished processing, it has to be re-coded - which will result in a quality loss.