Exactly, how i use my shield too....Kodi works excellent for local files. However Plex is good option if we want to access the files remotely, when we are not at home network. We only need to keep our shield on standby and connected to internet.
But having said that, Plex dosent work for me very well. Every now and then, it fails to recognise the plex server and it becomes useless for remote access.
So if accessing files on network is on priority, non pro will work equally good and one wouldn't miss anything.
For accessing local media files, for me, Kodi is hands down better than Plex. Kodi is fast, stable and audio passthrough works better.