Bit of an exaggeration seeing as how the BNet Balance didn't even double the token's price in the US. Sure it was a massive spike (< 60k to 90-100k and still slowly climbing), but it wasn't the ridiculous jump you're talking about.
I don't even think the most expensive clients (Chinese/Korea) will hit 500k from this.
Why wait? Buy tokens now and redeem for BNet balance before it goes up any more. It's not like gold has any real value anymore outside of trading it for BNet balance.
You can use BNet balance for game time, so buy up to $350 Balance worth and then sit on 10 tokens. If you have any more gold, use tokens to add game time to your WoW account until comfortable, then buy back up to 10.