I think I read about 26 of the books as a kid and you're right that not all of them were good. I did learn which writers to follow for the most part, though. My favorite was Diane Duane who wrote The Romulan Way and is still THE expert on Romulans as far as I'm concerned. Other good writers were Diane Carey and Vonda N. McIntyre. Books like The Romulan Way, Final Frontier (which had absolutely nothing in common with the movie), Strangers From the Sky (written by Margaret Wander Bonanno), Enterprise (which had absolutely nothing to do with the TV series), The Wounded Sky, Dreadnought!, etc. really shaped my view of not just Star Trek but sci-fi in general.
After Star Trek V: The Final Frontier was released, I kind of gave up on the novels and started to lose interest in Star Trek in general. Just because it was clear that they were rewriting everything with no concern for what had already been established in the books. Which is EXACTLY what I expect to happen with the sequel trilogy.