Well I'm using this line in my vm.conf file:
args: -vga qxl -spice port=7200,disable-ticketing -device virtio-serial,id=spice,bus=pci.0,addr=0x9 -chardev spicevmc,id=vdagent,name=vdagent -device virtserialport,chardev=vdagent,name=com.redhat.spice.0
and it works OK. Maybe you need args: -spice...