A good reason, though it will cost you some disk space!
When I made that same migration two years ago I reprocessed existing images into Lightroom as practice — and yes, I still had the CNX2 to export from the NEFs if I wanted to or had to. But it wasn't long before I had all the "good stuff" reprocessed in Lightroom.
FWIW, I reprocessed those LR images as my LR abilities, notably local selection techniques, improved. I also reprocessed everything when Lightroom 4 — Process Version 2012 — came out.
BTW, welcome to Lightroom!
Jon Kandel A New York City Nikonian and Team Member Please visit my website and critique the images!