Yeah... I'm well aware of many of these claims.
Be skeptical when reading Intel's marketing claims though. A whole lot of those benefits listed are mixed between different aspects of "64-bit support". For example, multitasking performance improvements under a 64-bit system are almost entirely due to the OS and are only extremely marginally impacted by individual applications (as long as they don't ever violate their memory ceiling and need to page out to disk). Another example is the multi-threading stuff, which has extremely little to do with "64-bit" and can be accomplished in a 32-bit executable just as easy as it can be in a 64-bit. The entire beauty of the Vista64 method is that it runs 32-bit applications better than Vista32 in many cases. This has nothing to do with a specific applications' level of support.
In all apples-to-apples, non-biased, performance comparisons I've seen, there are two main factors that determine if an application will substantially benefit from a 64-bit native executable:
1. Memory usage (Photoshop, MySQL, and Crysis would like 64-bit executables, Notepad and Firefox don't care).
2. The mix of long-integer and double-precision floating-point math that is done by the application (video compressors and other "heavy number crunchers" benefit here, most general purpose home-user applications do not because they are all written with the 32-bit operating system in mind and more precision isn't needed).
EDIT: Again... I have no idea if building a true 64-bit EXE for MC would make any difference. I don't have access to the source code and can't run any profiles on it to see if it would. My guess is that it would in very limited situations, but that the extremely efficient memory management schemes they use limit the impact of any benefits to people with truly enormous libraries (and I mean huge). But that is just a fairly uneducated guess.