Yeah, I share the doubts. If Witcher Senses were just an improved TW2 medallion, then I wouldn't have cared. It being something you can toggle on\off and with a smooth transition is better than spamming a button and having Geralt caress his medallion over and over. But it was marketed as more. Hell, it was actually marketed. If this were just a more refined feature that highlights loot, there wouldn't be even any point in mentioning it. That's like emphasizing that you can add exclamation marks near quest givers. But it's been given some stage-time by CDPR, indicating they consider it to be something noteworthy. So far I'm not sold on the implementation.
It's been associated with investigation, but my understanding of that word is different than what has been shown. As a player I no longer pay attention when such a feature is available. I just turn it on and the game encourages me to move from one shiny thing to the other (in case there actually are multiple shiny things to 'Use'), until the rails appear that lead me without trouble to the destination. Like when finding Johnny, or the werewolf, or the cave thanks to the wine trail.
Take the wine example in the PAX video. A while ago when thinking about Witcher Senses and investigation, what I would have imagined is a very dynamic scene. Maybe with animals having walked over the wine real-time and creating many different paths for you to possibly follow, requiring the player to notice which one is human footprints, and which one is claws or hooves or paws or whatever. On this note I'll say that I'm not after something similar to Cedric in TW2, because if I remember correctly you couldn't deduct which path was the right one. Having something like that in a huge game, over and over, is worse than having one single direction. Having multiple directions that you can somehow deduct which is the correct one, however, sounds cool to me and engaging. There's some player involvement.
Now I get that some won't want to wander to no end and keep their experience focused. That's fine, and in that case, it's good that they have the Witcher Senses (and here's a confession: I'll probably have plenty of times when I'll use them myself, because when there's an option offered it's hard not to take advantage of it). A problem is that the game doesn't seem to offer you anything to go by, without the Senses. Again the wine example. After Geralt noticed that someone walked through the wine, he could have said, "He went north, maybe north-west. To a cave nearby? Perhaps a house." That leaves it open for exploration for players who don't want to rely on the Senses. It gives you a direction, which is important (aimlessness isn't appealing), but it's general enough for you to explore a bit, instead of it being a rail.
I'm aware that I could be dead wrong and that the Senses in the full game might be much more varied. But I don't think it's smart to speculate why and how a feature will be decidedly better than what was shown so far. As far as I'm concerned, what was shown is what we'll get. Especially when it's CDPR who consciously decides what to show.