Agreed. Civilization Fanatics Center is an extremely rare and unique gaming forum, IMHO, which probably does things better than most official game site forms.
I typically totally ignore Steam forums about a particular game, unless I can find no other source for a certain topic. I would think things might trend in a better direction on their forums, but seems to currently be used by novices.
One thing I really like about CFC is things stick around. I've seen links to the official Firaxis Civ5 forums from CFC, and received an HTTP 404: Not Found error when following the link. With CFC, what was written in 2001 is still here, and if you need it, you can still find it. Might take a bit of browsing of a few searches, but it's still there and discoverable if you're determined enough.
CFC also does a really good job of making things searchable/browseable. Steam forums are essentially just a few stickies plus topics in most-recently-posted order. Which is fine if you're there for the latest buzz, but not great if you are looking for in-depth info about a particular topic, which may not have been posted about for months, or longer. Google can help sometimes, but it's not as good as CFC's Advanced Search, where you can limit your search by forum, poster, thread name, or thread contents - I've found that invaluable for Creation & Customization topics. And the Downloads Database is pretty handy, too. IMO, it's more granular than Steam Workshop, in part because it's specific to particular games rather than more general categories. In short, Steam forums are fine for general/recent info, but for game-specific, in-depth info, the advanced features of CFC do make a real difference. And I agree, what's been built up here over years isn't easy to equal in official forums, especially since a lot of those are only maintained while the game in question is selling well.
I do wonder what the impact of Firaxis/Steam forums for future Civ versions will be. Civ5 traffic has not been as robust as Civ4 traffic, and I suspect Steam forums/Firaxis forums are part of that reason. It's not so much CFC fading into oblivion that I'm concerned about either, so much as the epicenter of a future version moving to Firaxis forums/Steam forums or workshop. To some degree, the Workshop has already done that with Civ5. And while I absolutely agree it's very convenient - even more so for games with multiplayer servers where maps can be automatically downloaded from the workshop - I do have some reservations about whether that will impact the kind of large-scale, epic mods and total conversions we've seen for Civ3 through Civ5.