While working on material for VoG I noticed that Thaumaturgy was beginning to move too close to center stage, and this simply would not do.

While the game is meant to have a healthy dose of the supernatural, as well as yummy pre-apocalyptic goodness, it was all becomeing too much, so I did the simplest thing I could think of. Cut it out entirely.

However, I would still like the PCs to potentialy have access to some minor supernatural abilities, and so I've decided to sprinkle some supernatural goodies into the Advantages and Drawbacks.

Problem, very few supernatural abileties are purely benefitial or harmful.For example, A Touch Clairvoyant might have an easy time solving mysteries, but will likely have to check for sanity loss many times more often than the average person. And if you decide to tell people about your ability your going to be laughed at, potentialy damageing your reputation for ever.

My question in the end is, would single "power", supernatural merits give me the result I'm going for? Or would it end up being more of the same in the end?

Give us some context; what are you trying to do with Gaslight?

By your example I'm guessing that you want to depict the supernatural as unpleasant and not actually believed in by many; if this is the case, then I suggest that you want to collude with the players to make supernatural abilities unpleasant for the characters. Rather than punitively slapping the mystics with sanity checks and so forth, I believe you can create a less violent play dynamic that generates the desired look-and-feel more effectively by making both the benefit and consequence of the supernatural player tools.

For instance, here's how I might handle clairvoyance in a Cthulhu-ish World of Darkness game:

Clairvoyance
Whenever you fail a Social roll, you may spend 1 Willpower to activate Clairvoyance. This means that the reason that your character didn't succeed in his Social task is that he was distracted or unsettled by a sudden and unpleasant vision, making him lose his attention or putting others off with his odd behavior.

If you fail a Social roll when you have 0 Willpower, the character falls twitching on the floor, unconscious.

Each time you activate Clairvoyance, choose a topic for the vision, but do not describe the vision. Each half-remembered vision adds one die to rolls for obtaining information regarding that topic, until the end of the story; the broken images direct the character's attention along appropriate lines.

So, what this does is give the player some amount of control over his ability, but it is still partly out of his hands, and it bears a noticeable element of risk to underline the "unpleasant consequences" aspect. Most importantly, its effect in the gameworld is unverifiable externally; only the character knows why he occasionally has seizures, and only he knows why he's such a good detective.

I wasn't intending to simply slap all mystics with extra sanity checks. With my example of a the extra Sanity checks would only be a symptom of being exposed to more sanity degradeing stimuli than a normal person.

As for the feel I'd like to have for the supernatural. I would like it to be at times beautiful, at times hidious, sometimes malicious, more often simply amoral, and always Alien. However, unlike the WoD or CoC it is not primarily a horror game, though you can use it to tell horror stories at times, rather I'd like to keep it a more social game, with some pre-apocalyptic loomings.

I'm likeing your idea about makeing them both player-tools.It is definatly spemthing that fits with the game, even if it had not occured to me to have the consequence come "first".

What do sanity checks do in your game? Is sanity loss essentially a time count until your character is no longer playable (i.e. has gone nuts)? Or is it a system whereby interesting complications occur? In my mind, the distinction is important because in the first case you've got the higher power, lower shelf-like mistake that was AD&D's demihuman level limits whereas in the second you've got a trade of power vs. complication - and that's an interesting trade, or can be.

Both, actualy, every time ten levels of mental "damage" have been taken you either loose a level of perminant sanity, or take a perminant flaw (which is your mind copeing with what happened to it), it's supposed to be a GM and Player descision at the time it happens, whichever makes the most sense for the storyline.

It is still a little rough around the edges, and I may remove or drasticly alter it after some play tests.