RE: 'Wouldn't it being rare make it more valuable'
My point is; Steem is rare at the moment, but it won't be. It's rarity is currently driven by demand and supply.
Tulip Mania Was driven out of similar economic factors, both demand and supply contributed to it's rarity. It was an example about how short term rarity does not make something highly valuable in the long run..
No, your assumption is that it won't be rare, and I'm not sure what you base this on. Any marked increase in supply will be indicated by a wholesale spike in power-downs taking place, which would be quite easily identified seven days prior to the supply being put on the market.
True, short term rarity can never sustain long term. Fortunately, STEEM has far more fundamentals that lend itself to long term growth and sustainability in both price and user base.