My TNG spec script had a very similar premise to "Quality of Life," which aired 10 days after I sent in the script. The plot involved Data discovering and defending a new form of pseudo-cybernetic life, and he even caught on to the idea that it was sentient the same way in my script that he did in the episode -- because of a comment Geordi made as a joke. (Fortunately, I was able to recycle the concept of the life form, in modified and much more interesting fashion, in Greater Than the Sum
And one of my first DS9 pitches was "Terok Hel," which was a thriller set on a station of the same design as DS9. The next season, they did "Empok Nor." That made me go "hmm" a bit, but I realized I was probably far from the first person who pitched "Let's do a story set on a duplicate of the station so you can save money on sets."