Why not use a $15 with Gateway antivirus. What is the difference between a $15 router or a $150 router (features adn capabilities mostly).
Just imagine scanning for viruses before data reaches your android/windows phone (or phones), XBOX, Windows (various PC's Laptops, etc). an additional layer of protection!
For each PC owned, the cost for a good antivirus is costly or using Free ones, they tend to bottleneck PC Performance. of course, the router wouldn't need to sweep the internet (I'm sure clever retrovirus scanning bots could do just as well IF you wanted to make the whole internet safe) but lets face it, I wouldn't task a $15 router to that, just as long as my side of the network is clean.
Unlike requesting Spam assassin added (the mail server can manage that task) GAV is a great idea (since there is no central web as opposed to a centralized mail server for your accounts to pass through)!
even if GAV was configured to a NAS to store data/configs/etc.