^^ Aside from an Arch & Design material with glossy refraction, there's only one other method I know of for creating a diffusion effect that looks half way decent. You can apply a falloff opacity effect to the objects behind the bussard lens which makes their edges appear fuzzy. That's the method I used on my old Vanguard
model and my original TOS Enterprise
model. It only works well with certain shapes, however, mainly spheres, where the surface is guaranteed to curve away from you no matter what the viewing angle. It also fails to cast realistic shadows from the sun or whatever the light source happens to be (when, for example, the nacelle casts a shadow onto the secondary hull or interconnecting dorsal).
Something different: Would it be possible to make a small render with the warp glow of the nacelles disabled?
I'm very interested in how the cyan collector looks without the blue warp grille behind it; perhaps that would make things 'pop' again, as some have said. I have a suspicious feeling that the curves you've added around the grills are visually interesting enough, but I don't know for sure.
I think the bussard color has been decided and we're sticking with red. Besides which, I have no intention of leaving the warp grills dark.