I've re-read plenty of the New Frontier series...particularly the first four mini-books. I also re-read the first four VOY-R books in preparation for Kirsten M.F. Beyer's Full Circle and subsequent VOY-R books. Not really necessary, but worth it none the less. I've also re-read KRAD's A Time to... book, Articles of the Federation, and A Singular Destiny each once.