It’s an oft-repeated maxim in writing that good ideas are overrated: a good writer can make a good book out of an awful idea, and conversely, a bad writer will take a great idea and usually turn it an awful book. A common story, first brought to my attention by Brandon Sanderson, tells the origin of Jim Butcher’s Codex Alera series. To quote Wikipedia:
The inspiration for the series came from a bet Jim was challenged to by a member of the Delray Online Writer’s Workshop. The challenger bet that Jim could not write a good story based on a lame idea, and Jim countered that he could do it using two lame ideas of the challenger’s choosing. The “lame” ideas given were “Lost Roman Legion”, and “Pokémon”.
The moral of the story, aside from “don’t make bets with Jim Butcher ‘cuz he really takes that shit seriously,” is: don’t spend too much time worrying about whether your ideas are good or not, when you could be using that time to write (and thus becoming a better writer in the process).