Joy of Simchas Torah:[1]

The joy of the Simchas Torah is a celebration of the G-dly revelation caused through the fulfillment of a custom of Jewry. The entire concept of Hakafos is a custom of the prophets, and is not written of in the written Torah and was not received through oral tradition, but was rather accustomed by the prophets. This is the celebration of the connection of the Jewish people and the Torah. It is the celebration of the Torah itself, above the oral and written aspects of the Torah. Therefore, the joy of Simchas Torah far surpasses that of the Simchas Beis Hashoeiva, and all Jews are able to participate in this joy.

Joy of Simchas Beis Hashoeiva:[2]

The joy of the Simchas Beis Hashoeiva was a result of the revelation of the oral Torah. The oral Torah is rooted in Chochmah, and is greater than the root of the written Torah, which is rooted in Binah. This is why it is connected with the water libation, as water is rooted in Chochmah. Likewise, the water libation is not written of in the written Torah, and rather is an oral tradition that takes part of the oral Torah. This explains why only the Chassidim and meticulous Jews were allowed to participate in the dancing of the Simchas Beis Hashoeiva, as their souls too were rooted in Chochmah, and hence the joy relates to them, as opposed to the remainder of Jewry.

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[1] Siddur Im Dach p. 269

[2] Siddur Im Dach p. 269