^ Doubtful, although you will also be able to run 64 bit programs also. Also, if you plan on upgrading at some time, be sure to run the upgrade advisor. It can tell you which hardware/software may be incompatible as 64 bit windows requires 64 bit device drivers. So, if your printer manufacturer doesn't provide a 64 bit printer driver, you will be unable to use that printer with 64 bit windows.
64-bit OS (windows) can offer additional performance for 64-bit-compiled apps regardless of RAM (think video encoding, photo processing, compiling, anything with number-crunching). But 64-bit windows apps are scarce. Even the enumerated categories have apps which lack 64-bit editions.
I would sugest you hold off your 64-bit exchange if your system is running well and change it only when your current install show problems. Also as hawkeye22 said, check your devices for 64-bit drivers.
The benefit of accessing the whole 4GB or RAM is too small comparing to time spent reinstalling with all existing apps.