Many seem to believe the sentiments you have listed but i think it comes more from our distrust for the government(and impending elections) than the fact that a city can be built from scratch. I have had this argument with many who say that Konza will be a white elephant. what they however need to study is how similar projects have been done around the world from south korea(8 smart cities) ,to malaysia,to singapore , to china and closer to home egypt.
what the government is saying in short is "Nairobi is already messed up beyond repair, we are giving you a chance to invest in an ideal city and giving you incentives to do the same" .they are saying this to both locals and internationals. Internationals seem to be listening more.
As with anything else I could be wrong but if im right, a lot of people will be kicking themselves in the foot in 2017 for not going in, and if im wrong, well.....life goes on and a few very rich organisations lose a small part of their investment. i believe the former will be the case.