Is it just me or did the introduction of scrypt asics actually make scrypt coins less valuable 
Imho, it's because it is now easier to set-up large mining operations where the owner dumps his coins for fiat.
With GPUs, mining was done mostly by those who believed in the values of cryptocurrencies (although it's not the case anymore even with X11 coins, as too many of them use multipools to get Bitcoins through them.)