How important is it to clean your drivetrain?
I used to work on a fleet of cyclists' bikes who used their bikes as part of their full-time job, where it was usually raining and dirty. I changed a lot of drivetrains and oiled a lot of chains over the years. That said, I don't have any kind of empirical data to say that doing x will make your chain last y% longer. But I can speak generally about the relative factors at play, and what is worth considering when you're looking at your own personal bike / fleet and trying to decide where to invest your time and money. 

First, it makes a huge difference who is riding the bike and how they ride. If they are a bigger person who likes to mash the pedals, they will burn through drivetrains much faster than a smaller person who tends to spin. Some people, the 200lb+, aggressive riders, needed new drivetrains every 2 months. A smaller, more cautious rider who tends to spin might take a year or more to wear out the same chain. 

Another big factor is what kind of lube you use, and what conditions the drivetrain actually experiences. The ultimate cause of the chain wearing out is the holes for the pins will wear out as the pins rotate under tension and sand or dirt works in, effectively acting as sandpaper along the inside of those holes. How you oil the chain, and what kind of oil you use, also plays a big role in how much dirt and grime get picked up. Personally, I think a wax lube is really good at keeping grime and sand out, and makes my chain last longer while needing less cleaning. I probably apply a fresh coat about once a month. But you might also consider using a dry-season lubricant and a wet-season lubricant if you experience big seasonal swings in weather. 

Ultimately, though, I think it comes down to how much you ride and what kind of relationship you want to have with your bike. Some people identify strongly as a cyclist and get a lot of personal satisfaction out of optimizing their ride and keeping their drivetrain and bike perfectly clean. You can certainly go the other way, I think the majority of people who own a bike will probably never clean the chain. Most people probably never wear through a chain, either. So if you do either, I think you're on the right track.