My opinion on Ninfas is that their service went down hill, and their prices were above average compared to the lack of service.
We went a few times on Sunday nights last year, and with almost no one in there, it was still hard to get service, drink refills, chips and salsas refilled, etc.. One of my favorite dishes, the Pechuga Chihuahua was almost $20.00. Granted it was two breasts, enough for a second meal, but it would have been nice to get a half serving for half price. I think the one in Waco even asked if I wanted a half order recently, which wasn't on the menu.
I think poor management which trickles down to service and pricing structures are the bigger issues vs an over saturation of restaurants.
I think more restaurants that have opened have created more options for patrons and people aren't willing to stand in line for an hour plus as often when there are plenty of other choices next door or down the road.