I very much agree with you, Phil. If Wikipedia would rather be other things than comprehensive, which in the last couple of years appears to be the case, it only makes sense to prominently link to places with different criteria and tradeoffs to us but with free-content licenses, especially if they're other Wikis.
It'd be one thing if we didn't want to look elsewhere because we wanted to have everything. It's IMO hypocritical in the extreme to be with one hand saying that there are whole swathes of factual content that we don't want, and with the other saying that no, we won't link to those other places either. If we won't give readers what they're looking for by policy (written or de-facto), we should at the very least show them where they CAN go for it.
I also see no good reason why it's not OK to, for instance, prominently refer readers to Memory Alpha but fine to link to Wikiquote. Favoritism towards WMF projects is not defensible, I think.
-Matt