The Simpsons is like the television equivalent of The Beatles. Imagine if The Beatles were still around 25 years after they started. Would their legend be a big?
Sure they would write a good song now and again, but mostly it would be diminishing returns, people comparing the new stuff to the old stuff.
And the legend would be nowhere near as big.

Simpsons had a glorious 5 or 6 years in the 1990's. Something went wrong in the late 1990's. It went really bad for a few years and it was a really sorry sight. Like watching a former great athlete with cancer still trying to compete. Then sometime in the last decade it began to get better. You did not feel sense of sorrow and dread everytime you watched it.
Now the Simpsons is like a band that has reformed not as vital or as good as it was in the past but your glad its there anyway, and suprises you now and again.
I dont think it needs any more seasons. It should have ended about 10 years ago. Have loved a lot thats come out in recent years but. I think its important its remembered in a great way!!