I don't know that you can claim that KNDL "failed." It was essentially a soft-AC version of Christian music, a little softer than K-Love. Those two stations occupied two of the only four high powered FM frequencies in the Sonoma-Napa county wine country for years. The Adventist college that ran KNDL decided to sell it - probably because, like many stations licensed to small private colleges, the money offered was finally too good to turn away, and the college was in a financial bind.
K-Love, on the other hand, moved to Sacramento, and embarked on an empire-building project of having what has turned into a national radio station, when the FCC rules were dropped to prohibit such expansions. They seem to have moved into any market they could, regardless of how many other non-profit religious stations were already trying to make a go of it there. Their model makes it unnecessary for their stations to be financially successful, since the operating costs are so low, with eveything on hundreds of outlets coming from one studio. I recall, in talking to one of their founders before even the Santa Rosa station was started, that his dream was to have a full power station in San Francisco. Looks like they've got everything but that - yet with an extensive translator network across nearly everywhere, people who really want to hear them have a chance at it now.
I suppose Minnesota Public Radio could establish a similar nationwide network of classical stations, given the "rules" the religious guys are playing by. They do program one of the most compelling classical formats I've ever heard. But I think MPR actually has a stronger code of ethics to not compete directly against other classical public radio outlets, unless they are invited into a market (like Sun Valley ID, one of the few places outside of Minnesota where they hold a license). Or else, as in Palm Beach FL, they just buy another station outright and spiff up the signal and programming.