Long text field's 'Rows' seems to be ignored by CKEditor 4

That's because Wysiwyg sets the initial height to 420px.
You can override that by implementing hook_wysiwyg_editor_settings_alter() and changing the 'height' setting to what you want.
The downside is that that hook is run once per format and not once per field, because the field instance isn't available at that time int the code.
Some work has been done in #507696: Allow individual width/height per field to alter settings per field, but nobody's had time to complete it yet and the current implementation is not so efficient, if I remember correctly.