Hi,
Hummm. Some progress.
Do this first.
Open a Finder window and go to the View Menu and select Show Path Bar.
This shows the folders and icons across the bottom of the window as to the location you are in.
Now open your User's Folder (the one with the Little House iCon)
Use the View Menu again and then the Show View Options (CMD + J)
At the bottom select the option to display the Library.
As you can see I also use Cover Flow and the various columns listed.
We have already tried removing the com.apple.iChat.plist that holds most if not all of the windowing info.
Can you go to ~/Library/Preferences and remove com.apple.imagent.plist and restart the Messages app afterwards ?
Has that helped ?
Next go to ~/Library/Caches/Messages/Pictures
This should show you all the Buddy Pic of people you have contacted on AIM, Google/Jabber, Yahoo and Bonjour.
Check that each pic displays as an icon.
This one is a long short because it harks back to issues in iChat and I have not seen it for a while.
Having said that I have this one this does not display and is zero Bytes.
Remove any pics that are like this and restart Messages again.
The Pics are refreshed from the various Servers each time you launch Messages (and any Buddy list) so they all have "today" as the date.
Any Improvement ?
You can use the icons in the path bar to go back to other folders.
Pick out the Caches folder and then find com.apple.imfoundation.IMRemoteURLConnectionAgent
Drag the contents to the Trash and restart Messages.
I have not noticed that this makes any difference to the display I see when restarting Messages.
Next do the same to the contents of com.apple.messages.TranscriptRenderingService
Restart Messages
Again for me deleting this and restarting Messages does not seem to effect the display of text in the main window and the summary that shows under the name in the left hand list.
I will wait to hear back from you with those few.
It becomes increasingly like a guessing game to work out which interferes which this function of Messages.
The Caches file for the Font Book tends not to be a single User item to discard.
8:47 p.m. Wednesday; June 17, 2015
iMac 2.5Ghz i5 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad