Alexa is USELESS.
Why does everyone use Alexa? It means NOTHING...
Alexa is supposed to be used to rank sites in terms of how much traffic they get, except it doesn't work very well. I have a site that gets thousands of visitors per day and is ranked around 170,000 and a site that gets a handful of visitors per day ranked 46,000.
Do not spend anytime or money on boosting your Alexa ratings.
PR (link building) is FAR more important and is the best way to increase the profitability of any website.