Imho, <Query> should be a block and then use, possibly repeated options inside that block to configure the behavior. You can then use the ignorelist feature to filter the trigger conditions and it would be possible to easily add other options in the future. For example:

<Query>
  Severity "Failure"
  Severity "Warning"
  Severity "Ok"
  IgnoreSelected false
  Statement "INSERT INTO …"
</Query>

Severity "Ok" and IgnoreSelected true would then match anything but "Ok".

Also look at how queries are defined in the PostgreSQL and DBI plugins.