Why should I buy 64bit hardware ?

I would like to build my own machine, which is going to serve mail (Postfix, Courier-Imap), web (maybe), files (Samba), proxy (Squid), for my home-network. I hope to have it running for the next 4 to 5 years, if the hardware allows. Since SuSE 9.1 will include 64bit software I'm considering to make the new machine 64bit. Any reason to go (or not) to AMD Athlon64 (or Opteron) ? Comments invited. TIA -- Met vriendelijke groeten, Koenraad Lelong R&D Manager ACE electronics n.v.