I agree with others that you should not bring it up. It is almost impossible to bring it up without being (not just sounding) condescending, because you would in fact be telling them that you know better than they what they should be doing with their money. But I also think you should not feel bad about not bringing it up, because I think you are mistaken to think that
Now it's gotten to the point that we're doing them a disservice by not saying anything.
First of all, I don't see any "gotten to the point"--the situation is what it is, it's not like some crisis point has been reached. All we know is that they spend a lot of money on things that are lower priorities to you than saving for retirement.
Second, your not saying anything is a disservice only under a lot of questionable assumptions: that this spending is actually destructive, rather than simply different from what you choose; that you saying something will magically change their beliefs and their behaviours; that this can happen without seriously harming family relationships.
Third, your calculation of "a half-million dollars per decade in driving between golf and target" is somewhat overblown. That $2k-3k per month includes a lot more than just golf and target, so even in the most optimistic scenario it won't go to zero. In other words, you're looking at saving them a lot less than a half-million per decade.
However, if there's more going on than you've described--say, if they fret about not having enough money--then *when they bring it up* you could respond in a neutral way, one that doesn't directly criticize them or offer unsolicited advice. For example, "That's why we quit golfing: we decided the fun of it wasn't as valuable to us as not worrying about the end of the month" rather than "If you didn't dropped $80 every week at the club you'd be in much better shape."