To me canon is the subset of things that appeared on screen that make the universe the most interesting.
So in other words, you only subtract out things that ruin previously established things. Like the destruction of Romulus or Trip's death.
Stuff from novels and games are only canon if they make the universe more interesting.
My distaste for NuTrek has more to do with deviation from TOS than deviation from the spinoffs.
-Gets a giant object not to kill him by pretending he's carrying Corbomite on board
-Convinces a sentient weapon of mass destruction to destroy itself
-Survives a Q-like being long enough to get its Mommy and Daddy to intervene by suggesting more entertaining ways to kill him
No wit, no tactics, no battle of wills. Just beam in and shoot stuff. Boring.