You're correct that we have 1 building with a rare room. But the Timeless Monolith room is "Standard" and can hold any rarity. The event building rooms so far are all rarity-locked though and this is the first event with a rare room. You could of course also win 2 goldsmiths.
I would guess it'll be about 3 events before we see another rare room (i'd expect them to roll through common then uncommon then rare again) - unless they're really trying to make sure everyone has rare lvl 1 dorks for phase 2 of allies in which case they might load us up with lots of rare dorks