Hmm, interesting thread.
To answer the OP, I think the difference between Trek horror and your normal derivative "saw" style horror, is that Trek horror, for the most part works great at being psychologically terrifying.
You standard slasher film usually is more worried about how much it can gross you out.
There is a huge difference IMO. The morgue scene in Night Terrors is terrifying because the scene just gives you enough thread to tangle your brain in a "WTF is happening" thought. You see the bodies sitting upright, but still covered under the sheets. What's underneath? are the cadavers wide eyed open? Staring at Beverly? Are they all going to get up at the same time?
That's some scary shit.
Most horror movies now are just about how can we top the previous scene of a very brutal and gory torture scene, like how much more detail can we get to see of some guy's intestines being ripped open while he's alive or some shit.
That is not psychological at all. It's meant to trigger intense disgust and gross you the fuck out.