Well, I've swapped out my original APs for a pair of the newest Apple Airport Extremes, disabling the routing functionality, turning them into vanilla AP / GigE switch combos. Setup is wonky because you have to go through Apple's Airport Utility rather than the more typical web setup. The benefit of all that, though, is that Airport Utility can show you a pretty skeleton graph of your local network topology, helping you confirm that you put everything together properly.

Anyway, everything's working properly. I seem to be the only guy on the block with 5GHz WiFi. When I'm ten feet away, it's awesome, full signal strength. Add one or two sheetrock walls, and the attenuation is quite noticeable on the signal meter, with my phone claiming to have better signal on the 2.4GHz band. I have no idea when it might decide to switch over, but in practice I now have many fewer dead spots in the house. At some point, I'll get or borrow one of the new MacBook Airs with the 802.11ac and then I'll run a stack of speed tests. So far, color me satisfied.

(I decided against the UniFi system, since I really do want to keep two APs around, and I really do want the 802.11ac functionality for the occasions when I have multiple GB of photos on my laptop that I want to push to my desktop. That would have made a UniFi setup much, much pricier.)