You've got some good points there qts. The point about memory addressing is quite valid, but the impact of being able to address more than 4 GBs of memory would only currently benefit users of high end servers and workstations. It will also require the use of a 64 bit OS. (There is already a 64 bit Linux port available and Microsoft is working on an x86-64 Windows version.) Maybe in 3 or 4 years 4 GBs+ of memory be in typical desktop PCs.
The only thing you're missing is that a 64 bit ALU or FPU is going to be inherently slower than a 32 bit unit. (Why do you think the P4 uses 2 16 bit ALUs running at 2x clock frequency? It's FPU is also inferior in design to that of the Athlon. It is done to allow higher clockspeeds and to reduce the number of gates. ) A 64 bit carry lookahead or carry save adder unit, which are typical designs used for high speed ALUs, would have up to 4x the number of gates as a 32 bit unit. It would not surprise me the least that this is the reason that the Hammer CPUs are currently running no faster than 2 GHz. What a 64 bit FPU gives you directly is precision. Greater speed is not a given when moving from 16 bit to 32 bit, or likewise to 64 bit.
Unforunately, I'm not a graphics guy, so I can't comment on the 64 bit color issue, but I would imagine that specialized software would have to be written to take advantage of it. I do know that currently 32 bit color does not actually use all 32 bits for color information. (If I remember right, only 24 bits are used for the color, the last 8 bits are used for alpha information.) There is one other big problem: Most graphics cards only use a 10 bit D/A converter when generating an analog output and most digital LCDs can only display 16 million colors (24 bit).
I hope AMD is successful with the Hammer. The Hammer processor is certainly as revolutionary in design as the 80386 or the original Pentium. Hopefully, like them, it will in time prove to be a success.