Not worth it. Athlon II X2 is roughly on par with Intel E5000 series...if you get a 2nd hand E5200/E5300 for around £20-£25, you would be easily able to overclock it to 3.6-3.8GHz (I've overclocked my dad's PC which has the same motherboard as you and overclocked the E5200 to 3.8GHz).
Add another 2GB RAM for around £20~£25.
And possible get the Arctic Freezer 7 Pro V2 for £15, that's only around £55-£65 in total for the same performance as that £175 bundle (but of course you would have to do the overclock yourself, but it's really easy on that board with the E5000 CPU.)
But really, if you really was gonna upgrade, go for a Quad-core or Triple Core at least.