Interesting idea, though I'm not sure why 1000 other people need to agree to make people want to encourage their use as a currency.
Even for people holding Bitcoins as an investment, it makes sense to spend some of your coins. First, if you have a bunch, you can't sell them all without crashing the market. Second, if they don't take off as an actual currency, your "investment" will be absolutely worthless. The only possible value Bitcoins have is as a currency. If everyone just holds, we all end up with nothing.
Bitcoins are a great currency system. Let's use it as one.
(Of course I do have a suggestion as to where to spend some:
http://bitcoinharbor.com)