What is the meaning of "Tocheles Tzadikim Simchah"?
Rashi: In the end, their hope is fulfilled, and they rejoice.
R. Yonah #1: Regarding desire for wealth and honor, it says "Tocheles Memushachah Machalas Lev" (13:12). The hope of Tzadikim is not so - "Sason v'Simchah Yimatzei Vah" (Yeshayah 51:3). Their hope is not based on their strength; they do not rely on their understanding, rather, on Hashem's mercy - "Betach El Hashem b'Chol Libecha v'El Binasecha Al Tisha'en" (above, 3:5). They do not worry if the hope extends (before it is fulfilled), for they do not worry about decreased wealth - "Tov Me'at b'Yir'as Hashem" (15:16). In any case they get Simchah from their hope. They are always happy to arrange their hopes (pray) to Elokim, and put their hope in His Chesed. As long as their hope is extended and delayed, they delight in Avodas Hashem with hope and Bitachon.
R. Yonah #2: Their hope is not drawn out. Their salvation is close to come. If what they hoped for will not come, the virtue of their hope will be a reason for benefits and Chasadim greater and more esteemed than what they requested - "veha'Bote'ach ba'Shem Chesed Yesovevenu" (Tehilim 32:10).
Malbim: Tocheles applies to something that will surely come, or it was promised to come in a known time. Tikvah applies to something that is not clear or guaranteed. Tzadikim have Tocheles; their reward is guaranteed without any doubt, therefore they are happy. This is the opposite of extended Tocheles, which is "Machalas Lev." Their hope for Chesed Hashem is always found and never unfulfilled.
Why does it say "v'Sikvas Resha'im Toved"?
Rashi: Their hope will not come.
R. Yonah #1: When their hope does not come, their hope is lost. There is no reward for it, for they did not trust in Hashem's salvation.
R. Yonah #2: This is a curse, like "Al Titen Hashem Ma'avayei Rasha" (Tehilim 140:9). Sometimes when the verse mentions the Midah of a Tzadik, it does not say that a Rasha is the opposite, rather, it curses his Midah, e.g. "Pi Tzadik Yanuv Chachmah u'Leshon Tahpuchos Tikares" (below, 31). Tikvah applies to hope that a matter come soon; Tocheles applies to waiting, e.g. "va'Yiyachel Od Shiv'as Yamim" (Bereishis 8:12). Even what Resha'im hope for soon, their hope will be lost.
Malbim: Resha'im do not have Tocheles, only Tikvah, e.g. they hope to get rich. It is not guaranteed, and their hope will be lost.
