I have a 64-bit version of Vista on my laptop with 3gb of 667 ddr2. Would it be worth it to get 4gb ddr2 800?

I just upgraded from 32-bit vista to a 64-bit vista. I have on my computer 3gb of ddr2 667 ram. If I were to get 4gb of ddr2 800 ram, I would be able to utilize all 4gb in dual channel mode rather than just 2gb. It only costs $60 on Newegg and I was wondering if the performance increase will be worth the sixty dollars. By the way, the rated FSB on my processor is 800mhz, does that mean my laptop will be able to utilize the whole 800 mhz of ram?