IME chain life varies a lot depending on riding conditions, no matter how good care you take of them. I'm pretty sure a 30-mile day in fine Florida sand and salt air is going to take more out of a chain than a 200-mile overnighter on clean Ohio roads.

So I wouldn't ever replace a chain based on mileage. Measuring the wear is easy. One of those tools makes it even easier, but a ruler only takes a few seconds longer.