Reconstructed Koine pronunciation is more difficult for English-speaking students to learn than Erasmian. That difficulty was compounded by my requiring students to learn the alphabet along with the standard English transliteration system, which is based on Erasmian. That said, students seemed to be having the most trouble with traditional problems: ν looks like an English 'v', but is prounounced like an English 'n'; ρ looks like an English 'p', but is pronounced like an English 'r', and so on.
On Saturday afternoon, at the end of our 9 hours of "language camp," one of my students described how her Spanish teacher in South America spent a lot of time just talking to them in Spanish. In retrospect, I wish I had done a lot more talking or reading in Greek, and a bit less time up front trying to get them to talk.
So while I can hear the question, "is it really worth it?", I am more convinced than ever of the importance of extended exposure to the sound of the language. I'm pretty sure that confidence pronouncing the language fluidly, if not fluently, goes a long way toward easing the challenge of facing and translating unfamiliar texts.