The 1 gig of RAM as standard should be in every new Mac, without exception. The number of people who think Macs are slow because of the RAM is quite high.
C2D has more pipeline stages an an extra Integer ALU, as well as an extra 2mb cache. Synthetic benchmarks show a 2% - 30% performance increase (in Windows, OS X would be similar) but on average I'd estimate 15%. In real life, this translates to a very small advantage. In fact, if the FSB of the motherboard is the same (667mhz) then the performance increase is even smaller and I believe this is the case with the current MBPs.
C2D is much stronger when it comes to video encoding. h.264 is 20% faster!
Having more L2 cache BTW, actually cunsumes more power, since you have a lot of transistors to keep powered. Core 2 Duo has almost twice as many transitors as Core Duo. Tests have shown that both chips consume the same amount of power at idle and load and that there is virtually no difference in battery life. Therefore C2D has a better performance per watt than Core Duo, but any extra life being squeezed out of the new MacBook Pros is likely to be efficiences elsewhere or better powermanagement somewhere.
If you have a Core Duo, it should keep you happy for some time yet.