In the grand scheme of things the increased costs are minimal, you don't buy a 1.5 if you count every penny and drip of fuel. Do you feel the extra power, oh yes, it is a very different drive to the 1.3, quick off the mark from a standstill as it does not have the Atkinson economy cycle and the extra 30 BHP certainly helps. The facelift modifications to the bodyshell (stiffer) and reworked suspension and steering makes it handle better and feel more "planted" on the road. Even if you are in pottering mode it is a nicer car to drive.
Would I go back to a 1.3? No chance!