is there a reason to upgrade growl?

[StingMe]

...but you don't need Growl installed to get notifications. - When developers update their application to support Growl 1.3, Growl will no longer be required for them to display a notification to you. Think of these updated applications as Growl, and the Growl application as Growl Pro. The Growl 1.3 SDK includes a framework which can display a notification, even if Growl is not available. Developers use the same API. Please see our documentation in the SDK regarding Mist. 

From http://growl.posterous.com/growl-13-a-su...or-changes