Heybud,
A thermocline can be a physical barrier for fish. Some fish cannont tolerate the colder water or the lower dissolved oxygen levels that often accompanies that deeper, colder water. They simply won't go down there. A bottom-laid aerator which breaks up that thermocline will intuitevely increase habitat which you mentioned. Of course this is a generality as pond dynamics vary from one to the next based on several factors. Maybe a fisheries biologist could chime in here.
As important, an aerator will help the pond assymilate the wastes produced by a larger population/community of fish. This will keep your water quality better and your fish happier.
