First of all make sure you have a Dual core Cpu, as you will not be able to install the 64bit versions of windows 8. There are more advantages to running a 64 bit Os.
The first is the amount of memory windows can allocate to run programs ect is much bigger. So less time dipping into the hard drive to fetch Data, so it makes things a bit faster. More memory allows you to run more programs withing windows if you have a fair amount of it.
Where as a 32bit os is more limited to memory allocation and size access.
You will be able to use more than 4 GB of RAM with 64-bit.
64-bit is the future.
The first 64-bit CPU from AMD was back in 2003.
More and more applications will be made for 64-bit.
Most programs and applications are still made for 32-bit.
Most games are still 32-bit.
Most programs and application are still 32-bit.
32-bit is faster on older hardware (Single core CPU)
You won't be able to see/use more than 4 GB of RAM with 32-bit.(2.75-3.75 GB usable)
You make it sound like 64 bit can't run 32 bit programs. That's WRONG. 32 bit programs run just fine on a 64 bit OS, just like how a 32 bit OS can run 16 bit programs. In fact, a lot of 32 bit programs have gotten updated to either have 64 bit versions, or to use more RAM if running on a 64 bit OS.
OP: If you have a computer that's less than 4 years old, getting a 64 bit OS is worth it. Future programs will be coming on it, for sure, in the next six years.