What are you planning on doing with the laptop? If you are going to play games, then yes the extra speed and added cache will help. If you are just looking to do basic office work and web-surfing, then it may not be as big a deal.
Aside from clockspeed and cache the main difference is included technology in they cpu Core Duo will most likely have viiv techology with is aimed at entertainment, quick power on and resume like a VCR and the Centrino Due will have vPro i think it is which is aimed at business' which alows remote management at a hardware level.
not sure if the extra 150 i would look at graphics card and screen size, things that cannot be upgraded that you would have to live with forever. RAM, HDD and (CPU with a bit of luck and magic) could be upgraded. Also new 45nm tech coming out soon wich are build around intels new mobile platform with more features. might be worth waiting thinks its only 40 days now to see what it released, this might even push down the price of these two system.