Gary,
So far, I haven't seen any information you posted, that's correcting or clarifying my post...lol. Your description of how to set a CWB is very similar to mine, although you suggest using a white paper plate, which I'd disagree with. If you use a paper plate, as soon as it absorbs water, the color of it will change, as it soaks up water. This is why I suggested using a styrofoam plate. I've never used a gray scale for setting a CWB, but have heard that in some circumstances, it'll give more accurate results.
As for RAW vs. Jpg, I didn't see anywhere that mentioned that the OP was shooting in RAW, so I gave information on how to set a CWB. Whenever possible, I try to get the photo as good as possible, before needing post processing. So, if needed, I'd always suggest setting a CWB before shooting.
CWB actually can work, when shooting RAW. The CWB you've set will be used, even in RAW mode, if you make the proper selection, in post processing. In PS RAW converter, when adjusting WB, one of the options it'll give you, when selecting a WB adjustment, is "As Shot." If you pick "As Shot," it'll use the CWB you've set. Otherwise, in RAW, yes, you can do a lot with WB adjustments. I prefer to have the WB as close as "correct" as possible, to limit the amount of post processing needed.
As for my Canon 7D, it's a much "smarter" camera than the RebelXt and therefor, much more able to discern and adjust to the blue, in our reef tanks. I've shot probably 100 tanks with it, ALL using AWB, and it's got the color correct every time. Most of these were shot in JPG mode though, not RAW. The only time I've set a CWB, with the Canon 7D, was when shooting 2 weddings and my daughter's Senior Prom pics. These were shot in JPG/RAW mode. In post processing, of the RAW files, very little WB adjustments were needed, in the wedding photos and no WB adjustments were needed, with the prom photos.
Lately, I've been shooting a few tanks, in RAW. I've not had to do any adjustment to WB, in PS at all. I'm very new to shooting RAW though, so am still learning. My biggest disadvantage is that I'm still very new to post processing and need to learn more about it.