On the matter of the Ethiopean Limu, have you ever tried the Ethiopean Yirgacheffe? I have found this coffee to be very similar to the Limu, but IMHO, better. Cupping notes can be found here - http://www.coffeesnobs.com.au/cgi-bin/yabb/YaBB.cgi?board=cupping;action=display;num=10923738 00
The reason I have brought up the Ethiopean Yirgacheffe is that this coffee is an old CS favourite, and we tend to have a poll often. I am sure that this coffee will be polled sooner rather than later, and Id recommend that you try it. You wont be sorry :)
And I second your call on the Costa Rica and Guatemala Antigua. We should certainly spend more time exploring the Central American jewels.