I was surprised to find out in the last few years there are more (mostly relatively youngish) 78 rpm collectors here in the greater area than I figured. Not very many overall and sometimes with rather specialized niche-within-a-niche collecting tastes but they ARE there.
To the point that at least one place out of town does attract enough interest to stage record hop evenings where the DJ spins strictly 78s only. (Something that has been happening in certain "in-crowd" collecting hipster circles in our capital Berlin for some time. But down here ? )
Otherwise, similar to what you say - I myself usually limit myelf to 78s that have never been reissued on LP or CD (or at least not on easily accessible reissues) - or ocasionally others that are so dirt cheap that you cannot resist, even if you have the reissues. But I don't go out of my way anymore to search high and low for 78s.
Am I mistaken or took it a comparatively long time for the Savory set to get sold out? Was this maybe too specialized fare for the typical Mosaic clientele geared more towards more (or much more) modern jazz?
At any rate, glad I got it when it was brand-new.