What I learned as an amateur writer doesn't necessarily apply to a visual, non-professional medium like photostories--
The "learn to write" books stress avoiding visual cues like bold or italics. All-capitals is an absolute dead end. The choice of words ought to convey the emphasis. Writing books even frown on exclamation marks as a cheap shortcut.
These books can run extreme, however (they have to be extreme to sell copy). My second-cousin, an English teacher, found my use of exclamatory sentences without exclamation marks jarring. [ ie: "You are mad, mad," he said. ]
That being said, multiple exclamation marks or multiple question marks are considered amateurish.
"What!? What?? What!! WHAT?"
But, our application, cartoon photostories, has less burden of "professionalism". If you want ten exclamation marks for comedic effect, I'd say it is appropriate.
But, yeah, crazy bold and italics all over the place can get hard to read. And multi-colored fonts are a drag.
We had a department secretary who would send snotty training reminders to the entire department in a rainbow of font colors, bold type, italics, different fonts, and anything an elementary school girl could dream up.