you are well meaning but you fail to answer you own question.
If you use your Mac or Mac based network for business, especially if you exchange files with other -emails are files ya know- then you had better have your Mac protected.
While you will not suffer the effects of a Windows virus, the person you pass it on to may and boy I'd hate to be blamed for infecting a client's network because THEY did not have adequate protection.
Your server and clients should be scanned continuously and be removing all infections, even Windows based ones.....
Antivirus applications - Do you need them?