I think it is important for govt to be seen to take action even if some measure will have little effect. It helps in the battle to prevent panic.
I think it promotes panic myself.
Of course they should prevent large public gatherings and limit travel, close workplaces and extend the holiday. That's not grandstanding, that's normal practice in outbreaks.
The grandstanding is the PM wearing a mask at a press conference and doctors in hazmat suits.
I gather it is considered common courtesy in some countries to wear a face mask if you have any sort of cold, it's not to prevent you getting something, it's to prevent you spreading something.
I've always seen people wearing them in London and I can't say I've noticed an increase in the last week or two.
I have bought some though, just in case!