I'm not sure it's such a great idea, and here's why:
For 15 dollars I purchased access to the documentary and the game (both of which are shaping up to be incredible). But what really convinced me to spend the money is the notion that for $15 i could become a supporter something great - a really sweet feeling if you ask me.
What I'm worried about is that many people will be interested in becoming supporters, but will be discouraged by the $30 price tag, and will go looking for torrents of the video documentary (and consequently game).
The problem is that even if the money collected from those willing to pay $30 compensates for the people who aren't, you end up missing out on people who could potentially become a part of the following- the people who will never torrent a double fine game.
I think the release of REDS is very special because it created a community. This same community is likely to support double fine in future releases as well - so by raising the price for entering the community, you ultimately lose potential passionate supporters.
That's just my two cents. With all that said, I just want to reiterate that I am madly enjoying all the content and can't wait to get my hands on the release.