Yes, good points. It would be weird for NPCs not to react while casting a spell mid-dialogue. Cast and forget would make a more convenient and plausible option. It would be interesting to get some extra bits of insight on characters with it outside of dialogue.
I would actually prefer if communication related spells (e.g. speak with animals, speak with the dead, detect thoughts) were available to certain characters permanently instead of having to be cast as a spell. For example, all druids can speak with animals, all clerics can speak with the dead, all warlocks with The Great Old One as a patron can detect thoughts, etc.. If items that could grant them existed as well then it would open it up for other classes as well. However, I'm not sure if that would be compatible with the game mechanics.
