The Shulhan Aruch (O.H. 90:9) says that one should make an effort to pray both at the synagogue and with a Minyan. Regarding praying in a synagogue, the Kaf HaHaim (K.H., O.H., 90:78), citing the Yerushalmi (Berachot 4:6), says that when one prays at the synagogue it is as though one is offering an unblemished sacrifice in a pure vessel. As such, even if one cannot pray with a Minyan it is much more beneficial to pray at the synagogue than to pray, say, at one’s home. Regarding praying with a Minyan, it is said (Berachot 8a on Iyov 36:5) that Hashem does not turn back the prayers that were recited in a Minyan. The Shulhan Aruch goes on to say that if one cannot pray at the synagogue, one should pray at the time at which the congregation typically prays.
The Kaf HaHaim (ibid:59), quoting the Shelah HaKadosh, questions how it is that Hashem does not turn away the prayer of a Minyan, but that many times it appears as though the community’s prayers remain unanswered. The Shelah, who references Rabbi Moshe di Trani (Bet E-lohim), answers by using the the blessing of “Goel Israel” from the Amida as an example. Even though this blessing is recited innumerable times a day and the complete Redemption has not yet occurred, there are many smaller redemptions that take place all the time, such as the Jewish people being redeemed from countless plots on the part of the nations of the world. Thus, just because a prayer does not result in something tangible or in an expected way is not proof that Hashem is not answering the Minyan’s prayers. Additionally, there are instances when Hashem does not necessarily act on those prayers, but rather keeps them, as it were, and then decides if they will be fulfilled or not. Finally, there is a view that all prayers are always heard and that sometimes they will only be answered in the times of Mashiah. From this the idea is reinforced that praying is a Mitzvah incumbent on everyone, regardless of the outcome.
Interestingly, even though praying with a Minyan is of utmost importance, the Kaf HaHaim (ibid.) says that there are two instances in which praying alone are equally powerful. The first is when one prays during the Aseret Yeme Teshuva, as this is an especially auspicious time. The other is when one cries sincerely while praying alone.
The Ben Ish Hai (Od Yosef Hai, Parashat Yitro, §2) writes that the closer to the Temple Mount one prays, the more likely one’s prayers will be answered. As such, the Kotel is an especially powerful place, particularly in light of the fact that he Midrash (Bamidbar) says that when one prays there with a Minyan, Hashem Presence is found there.
Summary: There are many benefits to praying in a synagogue and with a Minyan.