I think it comes down to how badly you need fans (if at all) and how much a decent new fan can be had for in your area.
Are you having temp issues currently? Any of the current fans going bad? The AF series are just basic sleeve bearing fans, so they wouldn't be much of an upgrade from the Rosewill fans. Also your case supports 140mm fans, so if you were wanting to upgrade or replace any of the existing fans, I would stick with 140mm.