Thought about moving to Thunderbird, but moving the mail and addresses looks like a major project.
I solved this problem by using an IMAP server. I had for a time pondered the idea of setting up an IMAP server at home to be able to use whatever mailer I wanted. The server that also serves IMAP fetches mail from different e-mail accounts, the mail is filtered with procmail (that also calls spamassassin to get rid of spams, and clamav to get rid of mails containing MS-Windows viruses) and then put into appropriate folders. Dovecot then serves these folders using IMAP. By doing this, I can use whatever mailer I want, using whatever operating system I want. All my mails are stored in one place, the IMAP-server.
What has this do with your question? Well, one way to move mail between two mailers is to use a IMAP server. You upload the mails from Evolution to the IMAP server, and then downloads them into Thunderbird.
If you have a spare computer to act as an IMAP server that could be an option, and you could switch between Evolution, Thunderbird, Balsa, mutt, or whatever you fancy.
A very condensed information about my system can be found at http://www.sm6rpz.se/mailserver.html
Lars -- Lars E. Pettersson <lars@xxxxxxxx> http://www.sm6rpz.se/
