I thought you used FW VM's for your breakout and not Edges? In either case, you can use HA or ECMP to have 2 FW breakouts for the DC, sat on different hosts for redundancy.
One of the main advantages of VXLAN is preservation (saving of VLAN's) as only 1 VLAN is used to transport all the VXLAN traffic. Not to mention the 1000's of VNI's you can create in VXLAN (10k max in VMware). I suspect this will grow with future versions.
I said before, not every software/tool is for everybody. If you aren't convinced it is good or you believe you have a better way, then I suggest you design your infrastructure in the way you are most comfortable. However, I believe NSX would benefit you, but I don't know the in's and out's of your infrastructure.