Massive DS9 fan here too. That's a really great point, I'm wondering now what the critical reviews of the time had to say on this.
On the Ferengi, I think they were interesting as an exploration into casual racism. Basically the Gypsies of their era, unjustly stereotyped as crooked thieves by those outside their culture. Also some mixed messages in the end seasons there, with the Ferengi basically assuming the core principles of the Federation, which was mostly uncritically portrayed as some default universal superior culture. For all their implied critique of conquest imperialism from the Cardassians and later the Dominion, the writers seemed to take little issue with cultural imperialism when it was the Federation doing it.