Hello,
I just saw this post and thought I would add some of my experience with the LS5000.
I use VueScan almost exclusively for other scanners, but after many trials settled on Nikon Scan 4 for use with the LS5000. In spite of its "quirks", the image quality is just plain better.
My workflow is to turn off Nikon color management and all other scanner adjustments (including ICE, etc.), and to get as close to a "raw" scan as possible. I scan in 16 bit, and multi-sample. For a special project like this one, I would multiple-sample 16 times. Though I scan a lot of Kodachrome, I use the RGB Positive setting.
Initially, I have scanned a HCT target with this workflow and made a custom profile. Then, when I scan an image, I bring the original scan into CS4 and assign my profile. The color in this file then reflects the color in the chrome very closely. Then I open in LR3, which reads the embedded profile but does nothing to the original. This way I get access to everything that was ever in the scan.
These scans are almost always flat, and almost never blown (NS4's exposure setting is automatic, but quite good). With 16x sampling I can get a good deal of detail from the shadows. I then set white and black points, and otherwise adjust. I have been very happy with the results.
Best,
Michael