I could have let it go, but you made two incorrect points here, and these were the only two points that you made. Your first statement, taken at face value, says that increasing blower rpm will not increase cfm. This is incorrect. The cfm won't increase proportionally to blower speed, but it will increase. Your second statement is also incorrect. Moist air, per unit volume has a greater specific heat than dry air, and thus holds more sensible heat energy at a given temp, OTOH, it isn't a HELL of a lot more. The advantage of dryer air is that you can set your t-stat to a higher temp and still be comfortable. The load on the system is reduced, not because of the lower specific heat of the air, but because the rate of heat infiltration into the space is proportional to the temperature difference across the outside surfaces of the structure. With a higher external surface TD the net load on the system will be higher, independently of moisture content of the indoor air. In medium to low humidity areas this isn't a big factor since indoor RH won't vary as much with changes in blower speed as it will in high humidity areas.
In high humidity areas you can lose efficiency by reducing blower speed or indoor coil size if there is very much air infiltration, since the latent load will be higher, thus offsetting any gain provided by running a higher indoor temp. Given a tight structure, the higher latent capacity system may be more energy efficient or it may not be. There are too many factors to establish a rule of thumb; each structure is unique, as are the preferences and habits of its occupants. You should target RH, and let efficiency run a close second.
Where RH isn't a factor, then increasing blower speed should be considered, but again there are many other factors involved, one of which is the additional energy draw of the motor at higher speeds, another being the increase in high side pressure produced by the extra load on the system. In most every case, what is done on the one hand to increase efficiency is offset by some other factor to some degree, so that small changes won't in general have a significant effect on overall efficiency. Changing blower speed is not however a small change and should be done only when indoor comfort is noticeably lacking, and only after the real problem has been repaired, that is, if incorrect blower speed wasn't the real problem.
The OP's question is essentially equivalent to asking "should I increase the air/fuel ratio in my vehicle's carburetor?"
