We are all glad to help.
Here's a fun way to illustrate the difference. The blue line is the Athlon II 630 x4 2.8ghz. The orange line is the Athlon II 240e x2 2.8ghz.
http://www.anandtech.com/bench/default.aspx?p=105&p2=114&c=1
On the multi threaded apps, the x4 is vastly SUPERIOR. The single threaded, they are generally pretty close trading wins, but nothing that buries the other. The other advantage for the quad is the benchmark system is going to be running a very clean OS to isolate how the CPU effects the program performance. So a virus scanner isn't running, all the programs looking for auto updates, downloads, web browsers open, all that isn't running for the test. In the real world, all these resource thieves will be running so the quad core will do better than the benchmarks show compared to the dual that has 2 less cores to share for those other tasks.
My take on this is, you have upto $150 for a CPU. Minimum, you need $58 for a CPU. You could justify a CPU upgrade within 2 years and have to shell out more then if you want or just let the system do its best and live with it. Or, spend $100, far less than the cap, for a quad core, and have a CPU that will run for much longer than dual before showing its age. The cost ratio to expected life easily justifies the extra $42 now and as more and more apps go multi threaded, you'll be prepared for them.
As for the TDP or wattage of the CPU, that's a stat that represents the most amount of current the CPU is designed to handle. The current generates heat, so the lower the better. 95w is very reasonable, but really, that number shouldn't be anything you're using to make a decision unless you're looking for extreme power savings. Performance wise, doesn't matter.