Thank you very much, David,
How about these sentences:
5) It is good staying here.
6) It is useless staying here.
7) It is not much use staying here.
Would you say they need a comma?
I don't know why '1' and '3' seem very bad to me and these three don't seem that bad.
I assure you that when I am speaking or writing I try to stay clear of this structure altogether and use the infinitive, just as you suggested.