Windows

Put the value of "No" in the key of the registry HKEY_Local_Machine\System\CurrentControlSet\Services\Browser\Parameters

In this way the computer never participates in browser elections.

It doesn't solve the problem of broadcasts because the traffic to call for the election is still there but there would be no response so you can expect at least some less traffic than before.

Broadcasts don't cross routers, so I'm not sure why you blocked ports 137& 138,But this is you problem.You blocked almost all NetBIOS traffic so nobody will be able to authenticate to a DC on another VLAN. When you create a VLAN on a switch it keepsall broadcast local to this VLAN, you don't need to block any traffic on a router.
Dmitri

I agree with DVN. VLANS are done within switches and have nothing to do with routers, unless by some remote chance, they are capable of VLAN trunking, but this is also a switch only option. Usually.

Routers do not propogate browser elections. They are kept on a local subnet. That what WINS is for. I don't understand how you say u filtered those ports, unless u used the no ip-forward command on the router. Do not 'filter' them unless the IP helper address is point to a DC.

I wouldn't worry too much about borwser elections, unless you have a serious traffic problem.