I wouldn't update to a major new iOS version (to avoid incompatibility issues), but there's no reason to turn off WiFi or not sync it. Like Google with Andriod, Apple has the ability to remotely remove apps from devices, but unlike Google [1] [2] I've never heard of them using it and I can't find any articles that suggest they have.
I assume that it's only for malware (given they haven't removed tethering apps, for example) so I wouldn't worry.