The Splunk Add-on for Oracle is a collection of sample SQL data inputs. There really isn't a lot there to build comprehensive dashboards from, in my opinion. Most of the data being collected in the examples either doesn't change at all (or very rarely), keeps cumulative statistics from the time of database startup (making comparison of different time ranges tricky), or - in my opinion - provides relatively meaningless data that is only valid in the split second in which it was collected.
Using Splunk to collect the kind of performance information you are describing isn't really possible at this time; there are much more specialized tools out there for that purpose. Not saying it couldn't be done with Splunk, but it hasn't been done yet. Splunk's main value at the current time - again, in my opinion - is in collecting log and audit data from Oracle that will allow you to identify and diagnose infrastructure level issues or external (non-SQL related) problems. For a look at how to create your own Oracle monitoring app, including sample inputs in a variety of styles and some dashboard ideas, try taking a look at this: Log File Analysis for Oracle 11g
