The impact of democracy on growth does not seem to depend on the level of development.
"There is no significant interaction between democracy and the level of economic development in any of the specifications. Thus the impact of democracy does not seem to depend on the level of development. Moreover, in contrast to popular claims in the literature, democracy does not have a negative effect for countries with low levels of economic development. In fact, all of the main effects of democracy for the lowest 25th percentile country reported in columns 1-4 are positive and some are significant."