I don't understand your reasoning here. Why would air cooled by a post-element inlet offer any less dense and tasty a hit than air that's simply heated by a cooler element?
Temperature dials/adjusters are just one more thing that can go wrong in a vape, and can be expensive and/or difficult to include in a design. A cool inlet could be very simple and reliable. And it could be a much quicker (indeed, instant) way to alter temperature. If you had a lever for opening and closing the inlet, you don't have to wait for the element or heat exchanger to cool down or heat up as you do with a voltage change. And with log vapes in particular, this can take a long time - as those with log vapes and variable voltage supplys will be able to attest.
Simply because there is more air to vapor ratio, you have more air mixed with the vapor extracted from the plant.
I think it is a good idea, and it is a simple solution to vary the temp but it is a tough one to implement effectively IMO.
Stems have different diameters and the air inlets have diferent sizes on the tube surrounding the heater in log vaporizers.. This would make it complicated to have a one size fits all solution. Or rather, it is easy to make it fit, not so easy to make it work the same way. As Alan said above, "
The roasting tube design plays a large part in the overall vaporizer effectiveness."
The best way would be something like a slide piece that has several positions, but you would need to measure temps for each stem and vaporizer. And i'm still not factoring in the draw speed which will also interfere with the temperature. It could be a cilindrical piece that would fit between the center tube and the stem.
IMO, i would rather have an removable circuit that would act as a temperature regulator and adjust the voltage in the resistance automatically since this way it would be much more acurate. Being removable would allow to me have real temperature control in any vaporizer. This would be ground breaking.
If i want an inacurate control, i can use my logs controling the temp with draw speed, screen height and control the air leaks joining the stem with the center tube.