If you like relatively new feature in Joomla! - custom.css (when custom.css will be uploaded in CSS folder of administration template, it will be automatically loaded), you can easily change the look of the template.
See this custom.css file. It is example of how to simplify the look of administration template.
https://github.com/PhocaCz/CustomCSS
Just download custom.css and upload it to CSS folder of administration template, for example to:
administrator/templates/isis/css/
Custom.css is automatically loaded in administration
I do not know if there's something missing. But if you are interested, then just extend it or create new own variant of it.
