I like this approach. Much like Candy Crush only gives you 5 lives at a time and then you have to wait to get more. When something is scarce and desired, it becomes more valuable.
I'm also in favor of increasing the account creation cost. The Steemit account has an estimated value of $185,635,587 according to steemwhales with 3M in liquid Steem. Raising the price a bit won't hurt them too much, IMO, though I don't know anything about their operating budget. Yes some other onramps may pay a bit more, but couldn't that also be seen as a natural balance to growing too fast too quickly? We're already seeing some sporadic issues with the front end so maybe a little temporary slow down is a good thing.