I have had a 64bit athlon x2 4800+ machine for almost a year now ($5,000 worth) and MOTU just within the last week FINALLY came out with drivers for the 24i/o and timepiece AV I have to be able to actually run them on 64bit. Needless to say I spent alot of money on a machine that I am just now able to upgrade to 64bit. I would definately recommend that you check to find out if EVERY single little thing you use has a 64bit upgrade available yet before you make the move.
video card
sound card
break out box
effects plugins
mastering program
EVERYTHING you use.
IF you can actually get your hands on all of the drivers and upgrades you need? Yes 64bit will prove to be a much better format for you I am sure. My friend did a test and recorded the same audio into sonor5 in 32bit and 64bit and the 64bit actually sounds better! (to me anyways) also it was recorded in 24bit 96khz sample rate. Good luck with the driver/upgrade hunting!