Can I Bring Cold Air from the Basement?

While running through list of the keywords people used to find my site on the web just in three days I've stumbled on these questions:
Bringing cold air from the basement. Can I bring cold air from basement? How do I bring up the cold air from my basement? How do I draw the cold air in the basement up to the second floor? How to bring cold air from basement to main floor, putting a return in the basement to get cold air?

Is this idea of bringing cold air from the basement have any merits? Maybe we are loosing a huge source of free cold air that we can cheaply use to cool our houses?

So, I've decided to get to the bottom of this. In order to do that I've conducted a test:
On the cold air drop (a cold air drop is a duct, which is connecting cold air duct with a furnace), I have two by-pass humidifiers (P. 1). So I've took both covers off of them and switched the fan on my thermostat to the on position (P. 3).

P. 1                                                                                    P. 2

At the beginning of the test the outside temperature was 91*F, inside temperature was 73*F and RH 59% . (RH - Relative Humidity). At the same time in the basement the temperature was 60*F and RH 56%.
In order to make this test as good as possible I decided to take measurements every 10 minutes and in order to circulate the cold air I've opened up all supply registers in the basement - all four of them.

Here are the results:
1:12 pm: Upstairs 73*F, RH59%
              Downstairs (in the basement) 60*F, RH 56%

1:22 pm: Upstairs 73*F, RH57%
              Downstairs 61*F, RH57%

1:32 pm: Upstairs 73*F, RH55%
              Downstairs 62*F, RH58%

P. 3                                                                                                             P. 4

Therefore, as you can see there are no changes in the upstairs temperatures, but maybe I should close the supply registers in the basement because they are just recycling the same air?
So, I went to the basement and closed all of them off and opened up the basement's door. After that, I took the other measurements:

1:42 pm: Upstairs 73*F, RH55%
              Downstairs 62*F, RH60%
1:52 pm: Upstairs 73*F, RH53% (Outside temperature - 92*F (P. 2))
              Downstairs 62*F, RH61% (P. 4)

As you can see, the upstairs temperature has remained constant for all this time. However, downstairs temperatures and relative humidity were changing every time I've took the measurements!
So, maybe it happened because upstairs temperature was about to rise?
Then I switched the fan back to auto and waited for another 40 minutes:

2:32 pm Upstairs 74*F, PH54%
             Downstairs 61*F, PH57%

Yeah! As a result of using basement's cold air, I kept upstairs temperature constant up to 40 minutes! Is cost of electricity worth running the blower? You decide!