Developing an app that has already been done-ish?

Hey everyone,

Would it be considered extremely stupid and a complete waste of time or only slightly stupid and a big waste of time to develop a webapp that has kind of been done before already?

The app I would be competing against is an iPhone app (no universal mobile-optimized version that I can find) but has been an App Store pick of the week and has done really well.

There are actually many apps out there that accomplish largely the same thing.

I would likely make just a desktop and a mobile-optimized version of my app to maybe get at a bigger audience.