How to use a inputlook to run several different indexes depending on which option the user selects on the drop down and then using the lookup to collate the different fields into one field which stops having to rewrite a query.
How about having a dashboard with 'drop-down' showing the list of possible application names ? . something like below where you can populate the values and setup default/initial values etc.. The application selected by user is then available in the "appname" token.
|inputlookup xyz | stats count by application | table application
//using value from token
You can then use the value captured in token to select required application/index/sourcetype from the lookup
|inputlookup xyz | search APPLICATION=$appname$