Broadway is so unpredictable that I think there are relatively few sure things (save for a show boasting a major Hollywood star). I think it still takes considerable gumption to move a show from an acclaimed regional production, Off-Broadway or London and it involves more acumen than simply writing a check.
Even with its rave reviews in Chicago, August: Osage County - with no known stars, a big cast, big set and a playwright making his Broadway debut - had to have producers with nerves of steel.
Night Music, as the first Broadway revival of a major Sondheim title and with two stars at the helm, is probably much less of a risk. Still, Sondheim musicals, new or revivals, don't tend to run for long and audiences often dry up after the core Sondheim fans flood the theatre for the first few months.
As for La Cage, I think it also takes some confidence to bring a revival here so soon after the last revival's failure and starring a British actor no one has heard of over here.
The amount of original work debuting on Broadway is relatively rare (though Race is a world premiere). Still, there's quite a bit of new (to Broadway) work coming, even if it may have debuted elsewhere: A Steady Rain, Superior Donuts, Memphis, In the Next Room, Race, After Miss Julie, Wishful Drinking, Fela!, Time Stands Still, plus a few more plays for the spring yet to be announced.
In the midst of a poor economy, it's quite something that both commercial producers and non-profits are not all taking the tried and true method. Incredibly, last season, with 43 productions, was the busiest Broadway season since 1982. 24 productions are confirmed for this season, with 11 more soon to be announced, and probably more that I don't know about yet. I miss the big Broadway musicals and exciting plays of the Broadway of my youth, but I still think Broadway is more robust than I ever expected it to be right now.
Begin at the beginning and go on till you come to the end: then stop.