Sure, I assumed there would be something of the sort; however, it is more of a dev tool than anything else. The average user won’t know what to do with it. Whereas changing margin: 10 to margin: 8 in a text file that can be seen within the app is simpler. Still would take some learning but is less of a burden on people.
There appears to be a to-do list here for the dev types on the forum 
:
https://wiki.gnome.org/Projects/GTK/Inspector
GtkInspector is already pretty useful, but it could be even better. Here are some ideas for things to work on, in no particular order. Your help is appreciated!