Whatever you guys decide to make your replicas out of, I hope you take into consideration what happened to the original shooting miniature!
I swear --- I think the toughest shooting miniature I've ever heard of was the 8-foot Enterprise from Star Trek The Motion Picture! It survived multiple special effects companies (including a DP who wanted to blow it up for real!), rewiring, repaints, storage, and display around the world.
Compare that to stories about other models that just haven't held up all that well over the years or disintegrated in cases over time... Sure, the Enterprise was restored and repainted a few times but the basic structure has held up very well.
Surely, there's got to be something lightweight yet much stronger now that will hold up better than the material the original Cygnus miniature was made of...
(Now that I think about it, that miniature really does kind of look like the Eiffel Tower with all the criss-crossing girders right down to a similar "crown" on the highest spire! Creepy-looking, too. A real ghost ship... The end of The Black Hole gave me nightmares when I was younger...)