This is indeed getting out of hand but combating spam with spam is not going to be helpful for anyone.
Instead pressure valve with for example steam support tickets or trough the mailing lists to start revising the master server protocol so that these spam servers won't get listed. For example by forcing the server to initialize a ticket announcing its own IP and Port with the correct ticket generation mechanism they already use for the steam id's before it is listed.
For the time being for the Half-Life 2 Deathmatch players i have put a script here
that players can use to block all the known IP's which you can also find on that URL.
I am willing to expand this to other games as well if there is enough demand and valve is slow in fixing the issue.