Instead of shutting it down, you should leverage on your existing user-base for your next project. I actually had a similar experience, I created a hobby project as I learn RoR, and the project did take off with substantial traffic generated. However, the idea itself is not monetizable, other than pathetic AdSense. With this huge user base, I have created a second project, but this time with a solid business model before I started a single line of code. I'm channeling lots of traffic from the non-profitable project to the profitable one.