Actually, I'd say you did add wing area. The area beyond the old last rib wasn't really doing much to create lift. You replaced that with an entire extra rib bay on both ends, making the wing effectivly longer.

I say a better test would be to just chop off the UCD's tips and leave the wing with the resulting length. I can't speak from personal experience, but a couple of guys at my field have made that kind of modification to some of their fun flys, and all reported better handling as a result.

I'm not sure, but I think that some of those wing tips like the UCD has can have a bit of AOA to them, creating what ammounts to a little washin or washout at the tip. But since the "airfoil" of the tip itself is so thin, the effects are really small. Or, it's also possible that the "airfoil" on those tips actually stalls before the rest of the wing. Those tips are so big that I wonder if you can just write them off as "wingtips" and not actually take a look at the airfoil on them, and it's actions at various AOAs. I'm totally guessing here though.