@SourceSunTom, when you're ready to return, take a look at the zipped xcodeproj here for a different technique on processing the blurred dock.
This method bypasses the need to load the image into memory, send it to the GPU, scale, blur, cache, etc and just plugs directly into a private CG API to process the blur "inline" (GPU direct) on anything behind any subclassed instance of NSWindow. Adjust the alphaComponent value of an NSColor set as backgroundColor to the window.
It should fix the look of your blurred dock against a black background and remove the need to stretch and/or repeat the image when the dock icons scale up and down.
Next will be to figure out how to plug this same technique into the Finder's sidebar...
Cheers,
-AphoticD
View attachment 712894
EDIT: This technique requires a Core Image enabled graphics card. It failed on my PowerBook G4 Titanium (Radeon Mobility 9000) and Mac mini (Radeon 9200).