I went from an i7 2014 11” to a 2017 i7.
The additional screen real estate is worth the upgrade. Performance is supposed to be a little better on paper. Although I did bump it from 8GB on the air to 16GB. So that does give improvements to my use cases which is Xcode programming and occasionally running a Windows 10 VM. The rest of the time, the computer is used for word, excel, PowerPoint, and web surfing.
The keyboard is ok and easy to get used to. Just has the reliability concerns.
Why did I get the 12” over the new Air? Form factor... the 11” is a great little machine, that can be used anywhere, including trains, aircraft etc., with ease.
Always worth getting a decent amount of storage, so it can be used for a couple of years longer. Yes, you can manage storage via cloud services, and extra storage. But these can be awkward. Also, having less files on a larger disk, helps the ‘disk’ from being hammered, as the ‘wear’ gets spread over a larger capacity.
Certainly a worthwhile upgrade still; it won’t be any slower, and the display does make a big difference.