When it comes to hardware, most SQL Servers I have seen are over-powered. Memory and CPU are most often underuntilized. So when I'm asked whether a customer needs the 64-bit version of SQL server, I think it comes down to one question. Do you need more than 3GB of memory addressed?
It's important to note that the 32-bit version of Windows can only address 4GB of memory. By default, it reserves 2GB for itself, however this can be reduced to 1GB by using an operating system switch. Memory beyond the 4GB addressed by the OS can be accessed by SQL Server indirectly using the PAE switch.
The 64-bit version of SQL Server can address an incredible amount of memory directly, with no need of these work-arounds.