Will upgrading from a single core to a dual core make a big difference?

Running a Pent 4 HT CPU atm at 3.00ghz. Thinking of just doing a cheap upgrade to a dual core cpu (E5500 - 2.80ghz ] Etc etc. Wondering would there be a actual significant change in the performance of my computer? My ram is maxed out already. I don't want to spend too much on a brand new computer cause I don't necessarily use my computer so often anymore to invest in a better one.So what do you guys think? Will this upgrade give me a slight better performance?