I've seen way too many great family restaurants drop in quality over time. [Mainly because they stop being just family restaurants once they ate successfull.] Those nice delicious affordable restaurants are bound to gain popularity. They'll eventually start renovating, sometimes even expanding and thus also hire new staff. And they definitely earned it. But new cooks are super easy to notice since they're just pretty inexperienced and mess up even the basics. One example would be being served a completely burnt Schnitzel after waiting over 2 hours. Something that should have had a golden brown color was pure black. I couldn't even bother to complain after waiting such a long time and just removed the burnt layer.
And then you see all that nasty stuff that could be hidden in the kitchen on Kitchen Nightmare. In the past I wouldn't suspect the owners of anything like that but considering how little their kitchen staff care, it's only a matter of time.
I'd say 3 out of the 4 restaurants in my area actually got worse a while after renovating. The restaurants now look fabulous, and they can also charge more but the quality that each meal used to have just isn't there anymore.