Let the flaming begin.
Just kidding.
No, 64 bit processors are not needed, although we are getting close to the 4G direct addressing limit for 32 bits, Hyperthreading 3GHz processors aren't needed. 250G HDs aren't. None of these developments work miracles, but they advance the home PC's cabability.
AMD says 64 bits does not add greatly to the transistor count, if I recall. 64 bit paths or wider are probably already present in 32 bit CPUs. Floating point registers have always been 80 bits. What is being done is allowing programmers to directly use 64 bits. Similarly, the extra general purpose registers in the Athlon64 just allows programmers to use 16 instead of only 8 registers, when a much greater number are already present.behind the scenes. I saw recently that the hyperthreading P4 has 128 renaming registers, for the 16 general purpose registers which are accessible, 8 to each virtual processor. x86 CPUs can already address more than 4G, but only in segments, via selectors. 64bit or wider computing is alread with us, but mostly hidden from view, and inaccessible to programmers. For some reason, Intel does not want this capablity available except in Itaniums.