So it seems that OS X still has a problem with dial-up. I'm sorry to hear that.
My parents have dial-up also, and I was really disappointed with how 10.1 handled automatic connection. That was a feature they were used to from OS 9, but one that no longer worked after I upgraded their machine. They must have been bitten by the bug you described, because the machine would hang up in an endless loop I think when trying to connect that way. But they adapted and got used to the manual connection method.
You are obviously very knowledgeable about scripting your computer; wouldn't it be possible to approach the problem by scripting the connection rather than the disconnect?
I'm thinking of something like cron launching an AppleScript, which makes the connection with Internet Connect, then launches your Mail application. Is it possible?