To put a harness on the skyrocketed prices of vanities, just make new limited vanities more often.
When was the last limited item, lilipad, up for sale? Months, prob half a year ago.
If there are new limited vanities, say, once every month then people won't have to scramble for the few existing ones on the market. Again, law of supply and demand.
From the game developer's point of view, prob couldn't care less thou. Same here, while I agree that buying vanities now is good investment, I wouldn't want to contribute to this cycle that will raise the crazy prices further. Besides, if by any chance an update that might affect this come, the bubbles are gonna burst hard.