Would my iPhone 4 benefit from it?
Not as much as the 4S or the 5.
Be aware that the YouTube app has been removed (but you can get a Google version in the App store) and for maps they have ditched the excellent Google Maps and used their own which is still work in progress, still no Siri for you on a 4, its got over 200 hundred 'improvements' most of which you will be hard pushed to see or use
Its the first upgrade since Jobs passed away and it shows, its still rough in some areas
I'm staying on 5.1.1 with my jailbreak
for now