Hm, I keep the improvements if I switch the new first lines back to third person limited. That suggests it's less the pov switch and more the rewrite. There still may be reasons to switch, but it'll take more thought and experimentation.

(Perhaps first person makes it easier for me to write better? Or perhaps I'll see this jump in quality regardless as I rewrite? In which case it might be more a question of whether I want to differentiate this POV from the other two.)