Goodness knows that educators will forever argue over the best and most appropriate methods. A good, creative teacher will come up with activites that are effective no matter what their underlying philosophies and whether or not they use songs. And I just don’t think there are any one-size-fits-all methods.
Another point here is the difference between an all-day English or bilingual kindergarten versus three to four hours of “instruction” a week. The role of songs would be different, I think.
Personally, I think songs are useful at all levels. In my elementary school, we learned some songs both in English and in Spanish. So, we knew the meaning of the songs but it wasn’t translated word-for-word for us. In junior high, I chose to study Spanish instead of other languages because it seemed less “foreign” due to my early exposure. As I learned more, I could still remember words of the songs in Spanish and translate them for myself. My junior high Spanish teacher didn’t teach songs, but my sister’s teacher did. My sis sang the songs around the house and I picked them up. They helped to reinforce vocabulary, phrases and verb forms. I’m by no means fluent in Spanish. But what little I learned, I learned well, and I think the songs helped.
As I teacher, I’ve taught songs. I figure if I go to sleep with the lyrics running through my head over and over, chances are so will my students. That’s why I don’t like teaching very young students. I can’t stand having kiddy songs on constant loop in my mind. One problem with song usage in some kindy programs is that they teach a new song almost every class and try to cram in all of the new lesson points. Some teachers just plow through the songs like any other drill. Songs can be useful but they do need to be part of a larger curriculum.