I also have (past) experience with a network running MS/NetBIOS cruft
through routers with forwarding of directed broadcasts DISABLED.
It worked fine.
If there is some corner case I've missed that requires forwarding
of directed broadcast packets, it would be useful for that specific
case to be enumerated _in detail, in public_.
We ran MS Windows over routed network in seven localities without any type of broadcast enabled.
All what is needed for user transparent operation is to setup WINS.