You're missing a mid-ground alternative to full scale production and complete non-production. If you were to step down production on the lines you're realizing aren't selling at a more than desirable rate, but that you already have molds for, you could have a limited-production line where instead of producing them in regular status, you produce as-ordered, admitting for a time delay.
As to your statement that sprues are not easily stored on their own, I've not much of a knowledge in the field, I will confess, but the molds you use obviously would be, in their mated pairs, somewhat easy to store since they all fit to one dimension when together, thus could be boxed and stored in one location.
I'm not saying produce them on a regular timeframe, but it would give a happy ground for those of us who would like to buy some of the subjects you produce, those that aren't produced elsewhere, such as the TOS-1. If you went with the limited post-run production concept, it would allow you to conserve resources on producing the model versus full scale production, continue income on an already formed design, and continue to measure the impression of the customer base by how frequently the product is ordered. I don't know how it would look from your end, but it would seem to me, to be a viable concept. It allows you to retain a breadth of product, while limiting your main production lines. No need to expand too much.