Alexa ranking can be good if 1) You do blog and wanted to show off to the advertisers 2) Show that you have a lot of visitors worldwide Major Setbacks 1) Only people visit your page using the alexa toolbar will be counted
1. promote alexa toolbar use among your site-visitors by having your own alexa toolbar including your cleanly maintained siteinfo.xml 2. use yourself alexa toolbar ( IE / ffx ) to contribute to other sites' ranking
There is no value to your Alexa rank. First, less than 0.5% of all web surfers actually use the toolbar, so any ranking results it provides isn't valid. Alexa toolbar is more spyware than it is an ranking service. Alexa uses your data and surfing habits to sell to advertising companies and analysis companies to recieve revenue.
A lot of places sell traffic that will increase your Alexa rank. However, it doesn't have much value other than possibly publicizing or increasing the value of your website.
If you buy websites and include Alexa rank in your offer\price you need to re-evaluate the methods your using to put value on a website.