Here's another question: Is it safe to assume that the Caeliar do not know of the Q or other beings such as the Organians and/or Metrons? I ask because all three of these species would seem to be, at the very least, equivalent to the Caeliar and, in Q's case, superior to them.
It's not addressed in the trilogy; I'd presume that the Caeliar probably are aware of those cultures, but are more interested in finding one that exists on their level, as physical entities, rather than as pure energy (Organians) or extradimensional (Q). Also, the Douwd don't have a civilization so much as a few scattered individuals hiding among other cultures, the exact antithesis of Caeliar philosophy.
As for the Metrons, they showed themselves in "Arena" to be as reclusive as the Caeliar. It's possible the Caeliar are unaware of the Metrons and vice-versa. Of course, considering the Metrons' willingness to pit sentient beings in mortal combat, the two cultures might be philosophically incompatible; just as the Metrons considered humans to be savage, the Caeliar might hold the Metrons in a similar degree of contempt.
Yet the Caeliar speak and act as if they have no knowledge of the Q, et al. For a species that's had sentience for at least 65,000 years, I find that to be a bit odd, unless Q, et al., have deliberately avoided the Caeliar. If so, perhaps they found them to be a bit too ... stuck up? (Yeah, hard to admit, especially WRT the Q.)
I think what the Q might have found distasteful about the Caeliar is that they seem humorless, and their reclusive nature makes them provincial and, at times, xenophobic. Despite the sophistication of their technology, the Caeliar would probably bore the Q, in my opinion.