There may actually be a good reason why you're feeling guilty. And it may in fact be a better plan to do something else.
You can try the following thought experiment: suppose you follow through on this new business, spend 6 months working on it, and a month after it gets going, someone ELSE copies the idea, does it a little better than you, and your sales go to zero. How will you feel?
You might think, "Well, all's fair in love, war, and startups. I made a good attempt, learned a whole lot, and I got beat fair and square. It doesn't really bother me, that is how the game is played. Now I'll try something else."
Or, you might think, "Wow. I just wasted 6 months. I didn't gain any new skills. I don't feel good about what I did. I wish I had spent that time doing something to improve myself."
Or, you might feel, "I WAS ROBBED. I spent all this time working on a real improvement on web site X, but web site Y just ripped me off and benefited from my 6 months of hard work."
Never mind what you think is the "right" answer - you might be happier in the long run trying to think of something new, or at least spending your efforts on learning something new.