I went today to Oficina de Migracion in Cuenca to help a couple of expats with their visa extension and there's some changes in the process.
You still need all the docs: updated air tickets, letter in Spanish explaining why you want to stay in Ecuador, the application form, proof of economic means, a passport photo, passport color copy and movimiento migratorio.
What is diferent now is the passport color copy has to be notarized and there's no more in the building a police's office. You have to go to E. Muñoz street and Grand Colombia to get the Movimiento Migratorio document.
Good Luck!!
Vinny