Sure thing.

Let's start with the basic sensitivity. Imagine the difference between an animal that perceives the world primarily through sight (like humans) and an animal that perceives the world primarily through scent (like a dog). In both cases, the animal in question must learn how to make sense of the information collected. By way of example, imagine how terrifying the world must be to a person born blind that is suddenly granted sight (that's a thing and people really don't like it). It's like adding a whole new layer to the world.

You can have some fun with this. Say you have a player that wants the gift but doesn't have the XP for it and you have legitimately put together a series of situations that merit blossoming the talent. Instead of just saying, "Here you go, you have it at full," or "You don't have it until you pay for it," you can say that the cost associated with the Gift (10 XP) represents the learning curve associated with making sense of this new sensitivity to the world. Remember, points are the only real balancing factor in Unisystem so it behooves you, if you're of the mind, to track them rather carefully.

That said, I think it's a good idea to also add the more handy element of integrating Notice into sixth sense based Tasks/Tests. After all, it is about using your senses to gather information about the world and a gifted just happens to have an extra sense. I generally refrain from using Simple Perception because I think it should be for when you can use multiple senses to detect the same event. Anyway, I encourage the use of Notice and even Research/Investigation with the sixth sense, but it won't provide nearly the same detail that actual metaphysical arts can provide. However, since the sixth sense is a secondary sense for the Gifted, they couldn't use Tracking without some extremely obvious events. Like, you could use Tracking to find someone chased by an axe murderer with frequent encounters because of the lingering fear essence but you couldn't do it for someone that was just exploring because there isn't enough essence released from "wonder." It would be like tracking a person by scent. Sure, if the person drenched themselves in perfume and you were trying to find them, you could do something like that but a normal person without any particularly distinct odoriferous emissions would be well beyond your ability. You could do it with a tool and in the world of WitchCraft and Armageddon, those tools are the Metaphysical Arts.

So, while a Gifted with Notice, Research/Investigation, and Tracking could probably do a fair amount with their sixth sense, it would be comparable to what someone with a decent sense of smell could figure out. It's the various powers available from the Arts that really make things awesome. Things like Insight, Mindsight, Death Speech, and more allow a Gifted to really get into the details of the metaphysical layer of reality. And even then, you might want to bring back those mundane skills. In fact, if you opt for hard mode, you operate under the policy of "a chain is only as strong as its weakest link" and demand that they use their weakest link skill; if you opt for easy mode, let them use their best skills.

Moving on...

Insight is just one of the invocations that has been on my hit list. I eventually took on a strategy of reworking the invocations and that one was defined by the concept of "to see with eyes unclouded." I cobbled together a bunch of separate invocations into one, Scrying, and that is defined by "to see with eyes unfettered." I even retools Soulfire under the concept of "wield the smokeless flame (Essence)." That last one turned out to be kind of fun though I'm running a supers game so it hasn't come up.

So, let's go on to specific powers. For Spirit Mastery, I would consider a summoning based on the intent. Either a specific spirit is called and if it accepts, it's teleported into your presence, or you have to cast a general net and bring the nearest suitable spirit (or one that hears and decides to follow your spiritual lasso). This doesn't give the spirit essence, it merely provides enough of a lasso to bring it to you. That's why you generally want to have a ward in place or it might not appreciate being captured. It would be like lassoing a tiger but not bothering with a cage. Funny to outsiders, nasty to the guys that didn't think far enough ahead. Since spirits of the dead are not oathbound, it's not really worth pursuing the process of compacts. Note that this does not pay for the spirit to manifest, that's a whole other thing. This just makes the spirit come to you. In fact, forcing a spirit to manifest sounds like a worthwhile additional effect. Let me check if I have that in my version... I did not.

Death Speech 3 is funny. The time limit makes me suspect that it's not really summoning the dead so much as trying to dredge up the spiritual "fossil" of the entity and running some energy through it to get some answers. It's like a weird combination of Mindtime, Mindsight, and Mindtalk as it applies to spirits of the dead. Anyway, as before, there is no real way to hold the spirit in place with Death Speech so it may show up and just not cooperate (in which case you'll also want to decide if language barriers are a thing or if spirits can communicate in a pseudo-telepathic manner that forgoes linguistic barriers). In fact, the necromancer might even be able to bribe it with more Essence or the use of another power (like Death Vessel and a trip to a buffet or brothel).

There aren't a lot of human available powers that make a difference at this point but there is one that's kind of fun: Mindhands (I'm going to call it TK for Telekinesis). TK does work on spirits, but if you can't pinpoint the spirit's location, you can't very well grab it. So, maybe you have a magician friend of yours using Insight to spot a spirit, then lesser illusion to paint the spirit, then use TK to basically wrestle the spirit and hold it in place. Or, optionally, the seer has Mindsight and TK and can do this all by herself.

You might decide to make a spirit visible because it has been "stained" by the summoning (like how scientists stain slides so they can actually see the details of the bacteria or cells). It's kind of like how it's done in Final Fantasy: The Spirits Within (if you've seen it). It's your choice if it's visible to mundanes, though. I would say it is not but they are totally apparent to anyone with the Gift (no Task/Test needed, anyone that isn't distracted automatically notices). Again, still not visible. But a good summoner deposits the spirit inside a ward and knows it's there until the ward is breached. People not directly involved in the summoning may not sense it without some other power or ability that grants them the ability otherwise.

Clarity of purpose. Clarity of conscience.