I am lately curious about what effects it would have if there were 50% less minerals on each mineral patch. I am not suggesting this as a good idea or anything. I am only curious is all. How would it affect turtling, builds, timings, lategame, the general gameplay? Anyone interested in theorizing? 
depends. if there are the same amount of patchs but less minerals per patch, it just mean people will be expoing faster as the minerals will run out faster. If there are less patchs but same amount of minerals per crystal, then youll just see people expoing faster as minerals will run out faster. does that answer your question.
Would be zerg favored aka “hidden buff” which doesn’t really give zerg advantage in balance patch log but it would in general gameplay. The race expands fastest and has extremely good defensive options. It would turn balance even more to zerg favor. It’s pretty common that Terran or Protoss players at one point stuck on 3 or 4 bases (in extreme situations at 2) meanwhile zerg takes all over the map.
The minerals are more than fine, the drain fast, but not too fast!