Batch degrades OPEN time

During a vacation trip, I shot some short 320×240 72 pixels/inch movie clips using my digital camera’s movie mode option. Apple Quicktime Pro can convert a movie into an image sequence. So I made image sequences of the movie clips and put the 17,982 .png images into a folder on my

Machine Model: Power Mac G5
CPU Type: PowerPC 970 (2.2)
Number Of CPUs: 2
CPU Speed: 2 GHz
L2 Cache (per CPU): 512 KB
Memory: 3.5 GB
Bus Speed: 1 GHz
Boot ROM Version: 5.1.4f0

In Adobe Photoshop CS:

I defined the following Action: Auto Level Auto Contrast Image > Adjustments > Auto Levels
Image > Adjustments > Auto Contrast
File > Save for Web

which I added to Default Actions.atn and tried to process the 17,982 .png images via

File > Automate > Batch
Set: Default Actions.atn
Action: Auto Level Auto Contrast
Source: Folder
Override Action "Open Commands" (unchecked)
Include All Subfolders (checked)
Suppress File Open Option Dialogs (checked)
Suppress Color Profile Warnings (checked)
Destination: Save and Close
Override Action "Save Commands" (unchecked)
Errors: Log Errors To File

with the following

History Options:
Automatically Create First Snapshot (unchecked)
Automatically Create New Snapshot When Saving (unchecked) Allow Non-Linear History (unchecked)
Show New Snapshot Dialog by Default (unchecked)

The rate for the first 1000 images was around 35 images per minute. The rate for the second 1000 images was around 29 images per minute. The rate for the third 1000 images was around 20 images per minute. … After 14,000 images the rate was around 4 or 5 per minute. The processing time for an image remained at around 1 second throughout this. What increased was the time it took to OPEN the image. Doing a RESTART of my computer didn’t improve the performance.

Doing a normal File > Open command in Adobe Photoshop CS now takes several seconds where it would take less than a second before using File > Automate > Batch.

Is there something I can do (short of reinstalling Adobe Photoshop CS) to get this degraded File > Open time back to normal?

Is there some setting that I should be using with File > Automate > Batch to avoid this degradation to occur again?

Here is the other Adobe Photoshop CS environment data (not sure why it says I have 2048 MB of memory when I really have 3584 MB):

Preferences > General
Color Picker: Adobe
Image Interpolation: Bicubic (Better)
History States: 20
Options
Export Clipboard (checked)
Show Tool Tips (checked)
Zoom Resizes Window (checked)
Auto-update open documents (unchecked)
Show Asian Text Options (unchecked)
Beep When Done (unchecked)
Dynamic Color Sliders (checked)
Save Palette Locations (checked)
Show Font Names In English (checked)
Use Shift Key for Tool Switch (checked)
Use Smart Quotes (checked)
History Log (unchecked)

Preferences > File Handling
File Save Options
Image Previews: Always Save
Icon (checked)
Full Size (unchecked)
Macintosh Thumbnail (checked)
Windows Thumbnail (checked)
File Compatibility
Ignore EXIF profile tag (unchecked)
Ask Before Saving Layered TIFF Files (checked)
Enable Large Document Format (.psb) (unchecked)
Maximize PSD File Compatibility: Ask
Version Cue
Enable Version Cue Workgroup File Management (unchecked) Recent file l