Because it's interesting. Special effects are an art form, and it's worth studying the techniques of artists. Also because it's history. Learning or reconstructing the facts about things that happened in the past is worthwhile in its own right.
Exactly. While I wasn't that surprised that the TOS Troyian uniform pieces made use of commercial plastic placemats of the day, it was interesting that the same brand of placemats were used to make the Tholian as well.
Ditto when Fred Phillips told me that TOS Andorian antennae used cotton spools scavenged from the costume seamstress' workroom.