This episode also introduced us to the barely touched upon Iconian civilization. The idea of a very advanced race who could travel anywhere in the galaxy by merely stepping through a portal was quite interesting. Why did this advance civilization just die out when they had so much at their disposal to survive? Could an alien race we've seen in other series like DS9 and Voyager be descendants of the Iconians? I'll always miss that story potential.
The Iconians did pop up again (sort of) in the DS9 episode To The Death
Well, at least their gateways did.
I agree, I'm suprised they never revisited them properly to find out who they were though.