I haven't watched the show for half it's run now. I have seen a couple episodes from a few years back, however, and I, at least hadn't noticed any sort of quality dip.

The reason why I haven't watched it has nothing to do with a loss of quality, it's rather to do with me not having as much time to waste, or me wanting to find new things to waste my time with. If I watch The Simpsons, I would expect to be entertained, but I do know what I'd get by watching it so there's not much to be surprised by.

If I don't start watching it again at some point in the next couple of decades, I'll probably watch and enjoy the entire series once it concludes and winds up in all its 1,000 episode glory on a future streaming service.