Hi bart [finally!], and thank you again. Based on the two tests I have just done, I think I will take your advice on clear alkyd resin.
Here's an issue with the Krylon - because it goes on so thin and watery, the glitter bits "fall right through" it, right next to the back of the top sheet, and all flatten out against it; they are not "held in suspension", like a fly in amber, and that suspension and resultant multi-direction of the bits is what gives glitter its....glitter. When the bits at the "top" all flatten against the back of the top sheet it looks too much like silver spray paint. So Krylon is out. One thing has been settled for good! :)
So, two more questions for your very patient self - is the alkyd resin sort of thick? That is, once it is applied, and the glitter is added, will it suspend the bits or allow them to sink to the surface and flatten against the sheet? We don't want the latter...
Second, I'm thinking I'll just use the alkyd resin to affix the glitter to the sanded back of the top sheet, let dry, and then simply roll on a couple more layers as a sealant, no backing required. This is exactly what you did only your bottom would be my top [shiny sheet]. An alkyd base colour could be added between clear coats. The question is would this mean that only water-based contact cement could be used for applying to the shell? I.E. would solvent-based contact cement dissolve the alkyd? Sorry I have such a hard time getting these relationships/reactions straight...
If the alkyd is not suitable I will stay with acrylic gel, but it is going to be more expensive.
The great thing about the glitter I'm using is, it is actual glass with actual silver, [as opposed to hex glitter which is cross-cut from sheets of poly-whatever], so I don't think many adhesives would dissolve it. Relevant to that I have some "Glitter Brilliants" from Elmers from some early testing. The glitter is gold but a brash gold, too much. I soaked some in acetone and sure enough it removes the gold slowly, turning it a nice pale gold while not dissolving the actual hex bits.
Now I'm going to google alkyd resin for all it's worth.....
Mitch