Short answer, yes.

Longer answer mirrors some of what Vos has to say; most of the beauty in writing is the execution. A story certainly needs a setting that isn't tried-and-true to the marrow or simply uninteresting, but it's very possible to twist enough of a setting (be it the characters, interactions, events, miscellaneous bits) to make it different from another, even if in hindsight they may seem similar. In fact, that's something nearly impossible to avoid. Almost any trope or combination of tropes you decide to use has more than likely been done before. It's a matter of how you end up approaching them, and even beyond tropes, what you decide to do with the story. And I don't say things like this a lot, but I have plenty of faith in your ability to make a setting completely unique.

To be perfectly blunt, feeling hampered by others' works is a reason I don't read a lot of them. I tend to linger on what worked for them and then I just don't feel like writing much because... well, reasons you stated. On my part it's jealousy, plain and simple. So yep, it happens to people (to varying degrees).

One bit of advice I have is to let a story sit in your head for a while, and gather ideas as they come. I did this with a couple of my own stories because I was never truly confident in them (Origin's Eve and The Promotion, namely) and I ended up finishing them many months after first having the ideas. However, I've also completely dropped story ideas I've had because they felt too similar to stuff I've written. I had an idea for a macro/micro setting within a sort of early 1800's setting heavily involving pirates (and literal bilgerats for the micros) but it basically ended up being No Man's Land of the Caribbean. Did not feel unique at all, so I just decided to move on from it. However, ideas you drop may very well be worth re-exploring later on, when they've had time to sit--in keeping with that bit of advice.

Patience is difficult, especially when it comes to writing, but it pays off when in the end in the form of bulk and generally higher levels of satisfaction with what you have. Hopefully that little schpeal isn't too redundant, but it's stuff I've found helps.

When I gave up on stuff, it was typically because I had no clue where to go with it and lost interest in adding on, so I guess my answer to your question is no.

But using a familiar concept isn't bad or lacking in creativity. If anything, I view it as an enjoyable challenge to see how I can take an old concept and turn it around in a way it hasn't been done before. For example, Arbon referred to my Wolfsong story as the macro/micro meeting online trope as a pre-information age version. I went to a writer's panel recently hosted by published author's recently and they all more or less admitted that their styles and what the industry/audience looks for is "Same, but different."

Also, the Simpsons have done everything so you're screwed there.

Nope.

Even if I have/had the same idea as someone else, the execution is different. It might be the same concept/plot but the product is different, it reads differently, it engages differently.

So nah.

As a direct answer to your question, no. I've certainly felt discouraged or intimidated when I realized something has been done before but when I reach that point I usually just dig my heels in and try to figure out how to hell to subvert or put a new spin on well tread grounds.

When writing with a macro focus in particular, I don't know if there really is a lot of new ground left to tread. Chances are, it's inevitable that whatever ideas that can be dreamed up for a story are going to be similar, even in passing, to what has already been done. No shame in that, you've just got to put your own special take and spin on it. Be it your execution, setting, or dialogue. If you ever do get really stuck or intimidated, as Mannoth already mentioned, leaving ideas to bounce around in your head never hurts. Letting new ideas bleed into them, tackling it via different viewpoints, etc. Letting things sit and coming back to them at a later date usually proves helpful.

Yupp, know that feeling. All to easy to end up sidetracked with thoughts of who did this and who did what and how to make it different. The above posters got the mainstay of my reply covered, it just comes down to worries and trying to disregard them.

But personally I worry to much about loads of small things and the only times I find myself able to write anymore is the odd occasion when I somehow stop worrying. No worries about execution, content or even orginality - just writing for fun.