VISTA rules currently only have access to adjust pageview level items based on Adobe variables.
Wouldn't it be great if they could access visit-level data?
For example, if a user has called event1 and event2 in the session, then set eVar3.
Wouldn't it be great if they could access parameters OTHER than Adobe variable?
For example, if we've accidentally put values in the image request that are not recognized by Adobe, we should be able to use a VISTA rule to fix them. The image request may have eVar1=hello instead of v1=hello as the processing engine expects. Unfortunately, VISTA rules can't see this.