I don't have enough experience with the stuff to really evaluate your suggestion, but my (prejudicial) thought is no, one bottle of the right color should be all you need. Should more coats be necessary, use up the bottle. I think the bottles are sized so you'll have enough to paint a pair of (large) shoes; plenty for one or two saddles.
I painted one saddle with this stuff, a bright turquoise color that I thought might look good on my Holdsworth. The color came out a little too light, so I haven't used it
The deglazer is supposed to remove any existing finish so the paint sticks. I don't
think it has any effect on the color.
So... I don't know. Go for it, and post back! I'm as curious as you are.
I repainted a leatherette saddle with the red. and it came out rather red. Hasn't been used tough. I did also paint my rhm saddle a mix of blue and metallic silver, It's been used about a dozen times and has held up well. The color looks the same, and nobody's called me sparkle butt.
I'll try to remember to post pictures when Flickr works out the problem they seem to be having.