I have been to Ethiopia as well. It is a truly amzing place to visit. It has very strong sense of 'place'. When I was there I really wasn't reminded of anywhere else in the world. A feeling that is not all that common.
I would add a trek in the Simian moutains to a list of must. We did a 5 day horse trek. We saw saw troops of baboons more than 500 strong as well as a lot of birdlife. It was not as strenuous as it sounds.
In Addis we didn't stay in the Sheraton or the Hilton but in the hotel Taitu. This hotel was the first western style hotel built in Ethopia. It dates from 1911 and was very cool. The beds felt like they were from 1911 as well although I think the bed bugs were younger.
. For about US$7.00 it was an experience.
Yes Ethiopia is very poor but instead of being "horrifed" give something back by spending at local businesses and being genourous to the people you meet.