Pls see my book, which gives lots of examples of Eudora's scripability brokenness. You cannot expect rb-appscript or any scripting milieu to fix this. In AppleScript, you cannot say:
tell application "Eudora"
get window 1
Eudora just whines at you when you say that. So you can't say it in Ruby either.
As for your second example, it would help you to take time to read what I said in the article, or at least the rb-appscript docs.
eudora.messages.subject is a reference. To evaluate it, use