I keep my original ISP account going not so much because of the e-mail (which has mostly become spam anyway), but because a lot of search engines and link lists still point to my original website at
http://www.teleport.com/~afterglo, which was set up before owning domain names was universal. Despite all efforts, a lot of these search engines and link lists seemingly never respond to requests to update links. It just bounces traffic to the new site at
http://www.afterglow-photo.com, and that is worth $20 a month. It might be worth the money for at least a few months for you to keep the Earthlink account going, informing those who write you of the change, until you're sure most of the correspondents have your new e-mail.