A "block" card is an interesting idea. One thing to note is that Streaqs are locked, which is kind of like 5 "block" tiles (from your opponent's perspective). You can employ some strategy when going for a Streaq to determine what board tiles end up being "blocked". A little different than your idea, but similar.
Last edited by drewns; 10-19-2013 at 08:06 PM.