TOS and End User agreements are contracts to use a service or products, not a replacement for local laws. They're legally binding contracts, but you can challenge them, especially if the provider does something illegal or requires the user to do something illegal.
An extreme example that people like to toss around is a TOS that insists you kill someone to use their service. People are quick to laugh at this and say it obviously wouldn't be okay, but for some reason if it breaks consumer protection laws that are not well understood by the public, then that's okay and somehow "allowed" by the TOS.
But still I seriously doubt Valve will see a class action suit out of this, even if it could legally be justified (not that you actually need legal justification to file a lawsuit in the first place).
The real problem for them is a PR issue. In general, it's NOT a good idea to piss off the people who are actively spending money on your product. For that reason alone, I think they'll make an effort at making things right.
Personally I was looking forward to crafting away some of the Polycount dupes I had. I'd traded for the vintage ones, so the originals I bought from the store were sitting there unused and non-tradeable, non-craftable. At worst though, it means nothing's changed.
