Well, that's like saying To Do list apps are a solution with no problem, yet every few months there's a new favorite To Do list app that has some moderate success. So, I'd say that there is definitely a problem. It's not like people don't want / need to keep track of ideas. I would agree through that there are a TON of existing solutions. People keep track of ideas in notebooks and Evernote, etc. So, the pain point definitely isn't that high, but the solution I made is the best for me =]
I find it nice having an app dedicated to just my ideas, which also lets me categorize and rank them.