The Kitzur Shulchan Aruch (12:9) brings that "It is a great mitzvah to pray in a synagogue or in a Beis Midrash because these are sacred places. Even if it happens that there is no minyan, it is nevertheless a mitzvah to pray there even when praying alone, because these are holy places".
It is certainly debatable whether "lehitpalel" ("pray") in this case refers specifically to Shemoneh Esrei, but even as a broad guideline for all prayer it seems it would apply to the Amidah.
I assume ""Even without a minyan" to mean praying with a minyan is preferable to less than a minyan, and "even alone" to mean praying with fewer than nine other men is preferable to praying alone.