It's relative, I think.
I think of reader resonance in terms of the story and its characters sticking with the reader. I also factor in the probability of the book being re-read. In other words, while appeal is more applicable at the onset - Will people want to read this? Will it sound interesting to them? - reader resonance is the reaction after completing the book - Does the story stay with the readers? Do the characters stay with the readers?
It's easy to say that a book is GREAT! immediately after reaching the satisfying conclusion. It's right then, right there, in the moment of completion, so it might feel like it's the best book ever. But do you still exclaim a week, a month, a year after you've read it?
It's been years since THE ALISON RULES by Catherine Clark was published, and I still think about it. I still 'know' those characters. I still tell people about that book. The same with SWOLLEN by Melissa Lion, THE TRUTH ABOUT FOREVER by Sarah Dessen, and other titles. Some are bestsellers, some aren't. Some (THE GREAT GATSBY, ALICE'S ADVENTURES IN WONDERLAND, ANNE OF GREEN GABLES) are classics, some are contemporary. Some were originally published in a language I don't speak, making me thankful for translators (THE NEVERENDING STORY), and some have been translated in twenty different languages. Some can be found in most big-name bookstores and some are out-of-print.
Their publication dates don't matter to me. Their fame doesn't matter to me. Their covers don't matter to me. Other people's reviews of these books have no bearing on my opinion of these books. These books are here with me because, for one reason or other, they echo. Whether they whisper or scream, old or new, they are here with me for good.