Bimmerboi
Your system will be able to access all 4gb of ram, as you know, if applications are programmed for 64bit they will run faster. If the app is x86 i.e. 32bit then you may not see any or much improvement however you wont see much or any performance loss running 32bit apps under Vista x64
Most games work fine, as for other apps check with the vendor to see if it works under x64 same applies to hardware drivers, driver and application compatibility have come on leaps and bounds with Vista x64 and most vendors release the 64bit versions around the time they make the 32bit versions available
Best advice I can offer is google a comparison between vista 32 and 64 and see if ticks all the boxes you need and weight it up if it’s worth switching to