Some argue that day flights are better to upgrade so you can enjoy the service.
I would say night flights are just as if so not more important so you can sleep, unless you have a day at home to sleep afterward then maybe not as much reason but generally i prefer to sleep on the plane and not the whole day in bed when i could be doing something else.
I generally prioritise my sleep - whether that's day or night! I rarely get enough sleep when I'm on the ground, so being on an aeroplane is a great way of getting adequate sleep (and hoping for no disruption by noisy passengers) Being on an aeroplane was a huge relief when I was a Blackberry slave.
I would say that it's the matter of your priority - whether you like your sleep (then upgrade night flights, or all flights!), or whether you like the service/drinking (then upgrade day flights).