I don't know if you're an ebook reader, but there are a TON of old books set during the shows that are great and easy to get a hold of. Are you a long-time treklit fan that has read all the old ones, or are you coming to it now? Because the biggest reason that it doesn't bother me that few new books are set within each series is because there's always more to go find if I want them.
Just off the top of my head, Vendetta, Reunion, Imzadi I and II, Q-Squared, Immortal Coil, Masks, Q-In-Law, A Time To Kill > A Time To Heal, and Federation are all fabulous novels that take place either during TNG or in between TNG movies. (Federation is a crossover, and it also contradicts First Contact, but man it's awesome.)