Auto-update detection? That's pretty nice - now I see why you posted it before.
However,

      else echo -a 10Downloading and installing updates. Please do not exit mIRC until complete...

Instead of automatically updating, how about asking the person whether he/she would like to update or not. He/she might be already content with their script, but they'll most likely want to, so set what I had just said aside.

As for the dialog:

  did -r ageonvoice 4
  did -r ageonvoice 10

You can perform dialog actions through one command, such as:

did -r ageonvoice 4,10

If, for instance, you had something like:

did -r ageonvoice 3,4,5,6,7,8

, you could make it:

did -r ageonvoice 3-8

. This same concept applies when you have something like:

 did -r ageonvoice 3
did -a ageonvoice 3

...could be rewritten as

did -ra ageonvoice 3

If the dialog id name is too long, you could replace it with $dname.
I'm just saying for future occasions, which you might encounter. :)

As for the rest it looks nice, but instead of having multiple dialogs, why not add tabs to save space?