Shoftim, Devarim 16:18. Shoftim veshotrim.

The Medrash here brings the passuk in Mishlei "Leich ehl nemalah atzeil...asher ein lah katzin shoteir umosheil.... and says that one Tanna saw how an ant put down a grain of wheat and many others came and smelled it and did not move it away from its place, showing a sensitivity to gezeilah.

Mei’inyan le’inyan:
A member of my shiur, LW, remarked that the Gemora seems very sensitive to smells, both bad and good. I dismissed this as a trivial observation. However, see Sanhedrin 93b, where the Gemara says regarding Mashiach "V’nachah alav ru’ach Hashem..." and (Yeshaya 11) V’heirichu bidvar Hashem," which Rava interprets to mean that he is able to pasken by smelling the object or the person before him. Rashi there D"H Rava amar says that this is the pshat in the passuk of "lo l’mareh einav yabit v’lo l’mishma ozen yochi’ach," and despite that, "v’shafat b’tzedek dalim." How can he do that? By smelling the people or things involved. (I think that failing this test was a proof that Bar Kochva was not the Moshiach.)

Also, Niddah 20b, where R Elozor would smell mar’os and pasken.

I seem to remember that R Rudderman (maybe it was R’Moshe) that shtelled tzu another Gemara about paskening whether a certain kikar was tomei or tohor. I think it was the Gemara in Shabbos 138, where the woman took the kikar around to find out whether it was a rishon or a sheini when it was in an oven with a sheretz. I think he said that the only reason she would have to bring the kikar to the Dayanim was so that they could smell it.
In any case, you see that Chazal did attribute a certain spiritual capacity to the sense of smell.

Similar instances:

• "Rei’ach be’ni k’rei’ach hasodeh asher beiracho Hashem."

• Mordechai Hatzadik is symbolized by the K’tores.

• Amoleik is symbolized by to the fly that spoils fragrant oil.

• "Vayarach Hashem es rei’ach hanicho’ach" along with the din of Rei’ach and Nicho’ach by almost all korbanos (but not by Korban Pesach).

• Shir Hashirim 1:12, "Ahd she'hamelech bimsibo, nirdi nasan reicho."

• And, most interesting, the Gemara in Brachos 43b, where Rav is quoted as saying "From where do we learn that one makes a Bracha on a pleasant smell? From the passuk in Tehillim 150 "Kol haneshama tehalleil Yah." What is it that that the Neshama enjoys but the body does not? One must say this is the sense of smell."

Harav Shimon Krasner, mechaber of Nachlas Shimon on Tanach, tells me that the Tshuras Shai (a Sigetehr sefer of Tshuvos) discusses whether a dayan can pasken on the basis of information that he has b’ru’ach hakodesh, without any eidim or evidence. I suppose this is connected to the Lo bashomayim hi issue, and see the Maharitz Chayos in Yoma in the last perek, where the Gemara says that the Mahn helped decide monetary issues such as whether an eved belonged to Reuven or Shimon, and whether a marriage was still intact, where he mentions a sefer of his in which he proves that while a psak of halacha cannot be min hashamayim, determination of physical fact that comes min hashomayim can be accepted.

Now, without seeing his discussion, the Gemara in Shabbas 108a immediately comes to mind: the Gemara asks whether one may write the parshios of Tefillin on fish skin. The Gemara says, we'll have to wait for Eliahu Hanavi to tell us. The Gemara then asks, "and when he comes, how will that help us?" Rashi explains, because lo bashamayim he. The Gemara then answers, that the issue is only whether the 'zuhama,' the bad smell, ever completely leaves the skin. It is clear in this Gemara, then, that determination of fact is something that we can wait for Eliahu to tell us.

But then you have to wonder, if the issue is whether fish skin retains an odor, do we really have to wait for Eliahu Hanavi to pasken? Maybe he doesn't have a good sense of smell. Moshe Rabbeinu was a kvad peh; maybe Eliahu is a kvad ahf! And why don't we just go to Paris and ask one of the "Noses" that create perfumes? Perhaps this is another example of what the Gemara in Sanhedrin 93, mentioned above, is talking about-- that the Melech Hamashi'ach will have an exquisite sense of smell. and he will be able to tell us whether it retains an odor that passels for dvarim shebikedusha.

Also, see R Schwab here in his Maayan Beis Hasho’eivah on 18:15. He says that even Shmuel, the "ro’eh," only saw external fact, as we see when he thought Dovid’s brother Eliav was the king he was to anoint. He says that the ability to see into the heart is unique to the Melech Hamoshi’ach, and he brings the Gemara in Sanhedrin 93b and Rashi that he will smell the baalei din and know who’s chayav.

Thank you to Chaim B, who mentioned Reb Meir Simcha in the Meshech Chochma Breishis 29:35, Hapa'am Odeh es Hashem. He says that Reuven's name involves the sense of sight, Re'iyah; Shimon's, hearing; and Levi's, touch (yilaveh eilai ishi, contact.) On all these senses, one does not make a bracha. But Yehuda, whose essential nature particularly involves the sense of smell, as the Gemara in Sanhedrin brings from V’heirichu bidvar Hashem," this sense does involve a bracha-- hapa'am odeh es Hashem.

I don't have the Bnei Yisaschar in my library. I don't want one in my library. I only enjoy that kind of thing when it supports something I have from elsewhere, or when it is based on kishron and Chazals from Shas Bavli and the Medrash Rabbah. But when I get my hands on a Bnei Yisaschar, I'll report on his discussion as well bl'n.

Report on Bnei Yisaschar:
This appears to be his own chiddush. While much of what he says is tzarich iyun, expecially his kashe on the Gemara in Brachos, the following is what I gleaned from his discussion:
All the senses are listed in the sin of the Etz Hada'as, with the exception of smell. Therefore, the sense of smell was the least vulgarized of all the senses, and remains ethereal and, to some extent, spiritual. This is why we make a bracha on besamim after Shabbas: Motzei Shabbas is associated with Eliahu and Mashiach. Mashiach will have the unique talent of being able to discern spiritual qualities via the sense of smell. Specifically at the time of the geula this talent will become evident, because that is the time that the flaws of the nachash, the Zuhama, will be completely banished and reversed.

I know that Bloodhounds have a sense of smell that is like ten thousand times more acute than that of people. We're talking about a sense of smell that is associated with the rational and spiritual faculties: those gifted dogs will eat rotten fish and maggoty meat with pleasure. Evidently, the basic esthetic of their sense of smell is different than ours.