I took the upgrade offer on a LHR - ZRH one way earlier this year. Benefits were, lounge access at T5 (very nice), fast track immigration, increased baggage allowance, more space and better food onboard.
It was worth the extra cost with the offer, particularly as the wife had so much shopping the excess baggage charges alone would have been dearer. It wasn't worth the price difference when I first booked the flight though, that was way too much.