Depreciation is a problem on these bikes due to rapid innovations as you know. The 2011 Zero S and before had small batteries, brushed motors (with questionable reliability), and a top speed of 65 mph or so. 3 years later the same model is greatly improved with a newly designed brushless ac motor, 95 mph top speed, much larger batteries, etc. This made the 2011 nearly obsolete. 2012 was when there was a huge improvement in design and capability. Since 2012, the improvements have been less dramatic and depreciation is a little less dramatic. I own a 2013, but if I owned a 2011, I would trade it in. If I owned a 2012, I would keep it rather than go with a new 2014. The way to decrease your costs with these bikes is to run them a lot. Put many miles on them...then your per mile cost goes down. If you commute say 40 miles a day, that's easy to do. Also if you just like to ride a lot, it will put miles on the bike. I don't think it is a good investment for someone who just rides 1000 miles a year, but if you ride 20,000 miles a year, then the depreciation and initial cost are much less significant.
If you want a good, but cheap commuter and touring bike, look at the Ninja 300. It is a remarkable bike considering the price. If it is like the Ninja 250r it replaces, the depreciation will be about the lowest in the industry.