Android phones, apps and tablets

My HTC Sensation is on it's last legs and Nexus 4 16gb for £199 is still a fuck of a lot of phone for the money.

I'm on GiffGaff and with unlimited and or/ PAYG 4G data plans non-existant is there anything really making the 5 a must have over the 4?

Ditto.
My Sensation is hanging on by a thread.
Contract is up at the start of October and I'm not sure what to do.