I've used a compaq laptop that I was setting up with Suse Linux 9.1 for amd_64, and it runs a lot cooler than I expected, and for those apps that have native 64 bit version, you definitely do get a performance boost. So if you can afford it, a dual 64 bit system would be a real powerhouse for an audio workstation, but it can be difficult to get some hardware working, the 64 bit laptop mobos use a problematic yenta socket, so pcmcia might not work at all.
