To me, the range is the only place you can work on changes to your swing. To do that effectively, you have to give up worrying about where the ball is going, and focus only on what you’re actually doing. Slow motion, drills, short swings, that’s the best way to get yourself to change mechanics.
But if you’re not working on change, I’m not sure the range is as critical. I went through a swing change a couple years back, and I worked really steadily on it. Now, I use the range with the same drills to continually remind myself of the right movements. I also like doing full speed swings, just concentrating on alignment and tempo. Its easy to gradually get off, a little time on the range helps me keep those little things right.
I’m with @jon on one thing, I don’t like to spend a ton of time on the range. If I stop focusing on specifics, it becomes exercise and not practice. I try to get to the club about twice a week after work for a little practice. I usually stop in the tavern and get a beer to take to the range. I’ll practice, taking an occasional sip of beer, until the beer is gone. When the beer is gone, practice is over. That usually takes 40 to 45 minutes.