There is a pinned "Show Off Your Ship Designs" thread, though it's mostly died off.

I should note that it's mostly focused on aesthetically pleasing ship designs itself, as all you really need for a functional design is to slap some components on a hull.

True, although there might be some exceptions; for instance, were it not horrifically ugly, I might consider posting the most powerful ship design I ever created (in terms of attack/defense anyway). So there could be some cases where someone might post a functional design.

Also, I like to work components into the design of a ship, so that could be another reason.

http://library.galciv2.com/index.aspx?c=8

There are ships to download at that link, so I'm thinking that is the place you're looking for.

For as great as this game is, it's odd to me there isn't more activity on the boards and mod community, even this many years after release.  In fact, I put this game down for a while, and came back to it recently.  I expected a lot more archived content, strategy, mods, and discussions-- more on par with civfanatics.  Am I just missing some treasure trove somewhere?

No but the library has been broken for ages and as far as i have read here there is nothing in the pipeline to get it fixed. There are other sites that you can find ships on such as I-mod productions. They have a good range of them there, albeit most of them are in DA format and require you to alter them to get them to work in newer versions.