iPhone 4 iOS 7 seems to register more data used
Try iCleaner. This removes a variety of leftovers and other jailbreak files that can consume a lot of space. These files don't show in Usage as they are regarded by iOS as part of the system, but can be safely removed.

Cydia: it cleans up Cydia caches and temporary files, Cydia applications unnecessary files, partially downloaded Cydia packages and repo files.
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Log files: it deletes log files and crash reports from known locations. These files are generally irrelevant to the user and can be safely deleted.
Cache files: it scans and deletes system cache files and databases. Some of them are rebuilt upon respring. This helps removing obsolete cache data.
Temporary files: it deletes temporary files from your device. These files are meant to be removed automatically, but they often happen not to. iCleaner takes care of that.