Everyone has their own beliefs, but in general I would say: Build something users want, release early and release often, and spend as little money as possible in the process.

Build something you would use too. That way, you would also have that vested interest to improve upon it.

I agree. Build it for your need, but pay attention to how others use it and possibly tailor it for them as well.

Also, maybe, work on some sort of business model so you might be able to continue working on it.

build...sell...retire (just kidding)

Building a Product People Want (seems like PG's single golden rule)