Translation:Tonight we will drink less beer.
That too is interesting. From a purely technical point of view "vamos" is both indicative and imperative. Does imperative "vamos" need to be in the right position as in "Vamos tomar um cafezinho!"?
Perhaps "Vamos beber menos cerveja esta noite" doesn't sound like a command whereas "Vamos beber mais cerveja esta noite!" does. :-)
All your examples can be imperative.
But adding "esta noite" before vamos weakens that meaning so much that I'm having a hard time to see the imperative in that case.
For other persons, it would be necessary to add a comma:
- Esta noite, vá ao baile e só volte de manhã = Tonight, go to the ball and only come back in the morning (no... that's not their mother, certainly).
Even though, still vamos would sound indicative.