Let me ask you something, would you prefer working on an idea that already exists or something that's totally unique?
I think, most of us would prefer the latter. However, here's one important lesson that I've learned while working on Answerly.app
Its much better to work on an idea that's already there. Your product doesn't have to be the first in the market. Google wasn't first and neither was Facebook, Twitter, Pinterest, etc. I can go on with this list.
From an investors point of view, its much better to work on something that's already there - just try to be the better version of an existing service or platform.