So far in 2014 there have been a total of 177 medallion sales aside from the auctions which appear to be stalled. The last auction was held in March with little if any participation of the general public.
You should not buy a medallion with the notion that you will find a buyer when you need one.
The taxi business is at the start of big changes like the entry of the street hail livery; Uber; Lyft; much stricter and more punitive governance over the drivers and lengthy delays in hack license renewals and issuance. Over time these changes will push drivers to Uber snd Lyft or completely out of the driving profession. Recently the Deputy Commissioner at the TLC was hired by Uber after these Uber friendly changes took place.