It is imperative to well in NBDE Part 1 for many reasons:
1) to make the school look good! Schools take pride in this. Although dental schools don't rank publicly, you can bet that school rank amongst themselves year after year solely based on the NBDE Part 1 results
2) to specialize as you've mentioned yourself
3) you must pass to continue to 3rd year curriculum of dental school at some dental schools. Like for Nova, if you don't pass Part 1, then you can't continue to 3rd year.