On Bad things:
Some would benefit from improv classes if only to help keep them freezing when they make a mistake.
Others need to work on voice and intonation (suffering from the low-volume mumble or monotone that ruins so many academic talks). Again, acting classes could help (I take the grad students out into the woods once a year to practice speaking loudly.)
But most of the students need help in structuring their talks—in figuring out what the audience already knows, what they need to know, and what order to put the material in for smooth flow. That is not something that improv classes would help much with.