I'm not jealous of other people's plots, I think I have enough imagination, but what I do envy is how people translate their thoughts and their plots onto a sheet of paper and how it sounds so natural and effortless.
I don't think I feel jealous of other writers. To me writing is so personal that it's difficult to imagine trying to write as someone else. I feel like I have too many characters in my head already... In fact, it is difficult for me to read other's work when I am actively writing. It tends to distort my own voice on the page.
On the other hand, you probably get your work to the point where you are happy with it. Imagine how horrible it would be if everything you wrote was always uncomfortable for you to read. I get down after I finish something. It sometimes feels like a part of me is gone, like I've finished with this idea and now other pieces will be built on top...
Jealous? Of other writers? Oh, helz yeh. All the time. I'll be reading something and come across a beautiful turn of phrase or an exceptionally well developed scene and think, "Damn! I wish I could write like that." And then, I had that thought over one of those particularly nice passages and then realized, I DID! I was reading one of my own works. That, of course, made me think, "Hmph. Sometimes, I really can write."
I don't get jealous of those greater than me because I accept that I am not the best, nore do I have any strong desires to be the best. If I can entertain people with my writing than I am happy. Besides, greatness is subjective. Some books I admire, others find just okay. Same with movies. If I were to be jealous of other's writing, it would be of their prose, not their imaginations, which I often find lacking.