If you want the list of updates, I would advise to read the release notes for SR6 version.
Qlikview upgrade should be done if you have some bugs or missing features which were updated in later service release.
You're right, it is better to update IE plugin and Qlikview DEvelopper as well ( so that everybody is using the same version).
Installing a new release is (in my point of view) a mini migration but still a migration. I highly advise you to test applications on a test server using the release, because there can have strange behavior or issues ( for example calculated dimensions causes issues in SR6, etc..).
So to summarize, if you don't see any specific need to upgrade, don't do it... and moreover wait to migrate for V10...