True, but that doesn't mean doing additional work during the parse is free. Optimizing out static expressions will take additional time, and in general that additional time will be linear in the query size.

My argument is that, on average, it will more than pay for itself.

The only losing case, if there are any measurable ones, is where you have long queries and short data. I'd call that a case of "doing it wrong". Wrong tool for the job.