A pyramid scheme is any scheme in which early adopters profit only if new money keeps coming in. I don't think you want to argue that Bitcoin's price can grow without influx of new money - bitcoin doesn't produce anything other than more bitcoins and heat.
I have already explained why a rational player would invest in a pyramid scheme (buy BTC at the auction), but I'll do it again:
1. Buy BTC below market at auction.
2. Sell on exchanges at market.
3. Profit.
Ok, I understood your point. But, who says that new monies won't come in and people won't profit anymore? BTC is still in development mode and has a lot to capture...