I understand the idea of keeping exclamation marks in check, but is there more latitude in their use in the thoughts and dialogue of characters, the same way there is some flexibility in characters using clichés in their speech?

There is room to use clichés in dialogue because it is not uncommon for people to speak using such trite language. It has the potential to add authenticity and, for certain characters, reveal more about their personality. The same, however, isn’t true for exclamation marks. In fact, exclamation marks tend to be most often abused in dialogue.

While we might raise our voice or create emphasis when speaking, an exclamation mark tells the reader how to interpret a line. The writer’s job is to show that. Let the words do the work of revealing the urgency or upset. This might happen in the dialogue itself or in the narrative that follows. Often, a gesture or action done by the speaker—storming out of the room, fisting a hand—can compliment the dialogue in a more informative and meaningful way than punctuation.

Of course, this is not to say exclamation marks should always be avoided. Use them only when you need to and they stand a better chance of carrying the impact you intend.