File open/save dialog causes SPOD with 10.10.3

Question

Just updated to 10.10.3 from 10.10.2 using the combo updater (after hearing stories of people being hosed by the normal updater and having success once the combo was applied).
Now, however, I find that whenever any application needs to open or save a file, and the directory selected in the dialog has a LOT of files (like 10K files), I get a SPOD (spinning pinwheel of death) for minutes.  MINUTES.  This never happened on any previous iteration of any MacOS.  This is on a MBP late-2013 with 16GB of RAM and a SSD.  
Already repaired permissions.  Checked the filesystem with Disk Utility.  It's OK.
This is really debilitating.
I have a saved process sample output from Safari while it was in SPOD mode with the file dialog open.  I can upload this if would be interesting to anyone.  NOTE: just attempting to save this sample trace from within Activity Monitor caused that application to SPOD while it was asking me where to save the sample output.

Answer 1

When you see a beachball cursor or the slowness is especially bad, note the exact time: hour, minute, second.  
These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.
Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad and start typing the name.
The title of the Console window should be All Messages. If it isn't, select
          SYSTEM LOG QUERIES ▹ All Messages
from the log list on the left. If you don't see that list, select
          View ▹ Show Log List
from the menu bar at the top of the screen.
Each message in the log begins with the date and time when it was entered. Scroll back to the time you noted above.
Select the messages entered from then until the end of the episode, or until they start to repeat, whichever comes first.
Copy the messages to the Clipboard by pressing the key combination command-C. Paste into a reply to this message by pressing command-V.
The log contains a vast amount of information, almost all of it useless for solving any particular problem. When posting a log extract, be selective. A few dozen lines are almost always more than enough.
Please don't indiscriminately dump thousands of lines from the log into this discussion.
Please don't post screenshots of log messages—post the text.
Some private information, such as your name, may appear in the log. Anonymize before posting.