I've been dying to ask this question for a while but what does everyone do with all the rest of the model kits you buy once you have cannabilsed all the SS parts from it?
If you look hard enough you find that a lot of kit leftovers are used on other models from the same movie / tv show.
I've only had 1 model where almost the whole single kit is used, it was the AMT Silhouette which if you rearange the parts becomes a police car used on the old Thunderbirds tv show. It's also the only studio scale minature I've built that requires only 1 kit
I tend to build the kit if possible without the part(s) I used.
The Monogram B-29 is such a kit
If the kit cost a ton of money I cast the parts needed and then sell the kit after returning the original. Think Bandai Hummel or Otaka D51-101 which are over $100 each.
If the kit is used in a lot of models the parts are cast and the originals are placed in a "parts libary" to remake molds as needed. Think Airfix Saturn 5 or the 8rads.