It sounds like you've tried some very good remedies. A couple of additional thoughts:
Have you removed Game Center based apps? Game Center can run checks to make sure you are still a high scorer, etc.
Have you considered contacting your cellular carrier and simply finding an international roaming plan supplied by them? That would allow you to keep your number for texting and calls, but not have to deal with the pocket broadband. It sounds like you're just planning to use the texting and/or calls very rarely.
Hopefully you know you can check cellular data use at Settings > Cellular > Cellular Usage (near the bottom). You could dry run only using cellular data at home to see what is consuming your data. Or if you simply keep your home cellular service while abroad, you can monitor your progress while traveling.
Also see http://support.apple.com/kb/HT4146
Are there any more recent news on this topic? Maybe changes coming with iOS 8?
There are many scenarios, where you may use a limited connection over wifi (tethering from Android to iOS, from iOS to iOS, mobile access points, limited data plans at some relative's place, ...). Windows 8 has a setting to declare a wifi connection as metered in the Wifi connection menu. Android 4.1+ supposedly does this automatically, if the wifi source is another Android 4.1+ device, and otherwise has a somewhat hidden setting for that purpose. Both make the device treat those Wifi connections as if they were mobile data (and often they are).
On iOS7 at least I know no method to do the same, hoping very much for iOS8. (Note that while the intelligent-hotspot feature hopefully includes this, it is no help in any use-case, that includes a non-apple device).